Actually, I plan to complete the translation, but for today it is partial.
In 1851 Raphael Kirchheim - see here about Kirchheim and his cholent - was working on his annotated edition of the Seven Minor Tractates (link) as well as a work about the Samaritans, intended as an introduction to Massekhet Kutim (link). Before these works were finalized at the printer, he asked Shadal to look it over and give comment. Shadal replied that he did not have the time for that, but he would be happy to send him whatever material he had written about the Samaritans, based on his own researches. Most of it was written in Italian, but Shadal rewrote it in Hebrew. Kirchheim printed the entire letter as an appendix in his Karmei Shomron. It contains some interesting thoughts, and here is my partial translation:
I was overjoyed when I heard the news that you are publishing the Seven Minor Tractates, which for many generations languished in obscurity. Today is a holiday! - to find that you are printing them with explanations and notes; among them, your great book Karmei Shomron which, through your broad learning, you elaborated on the history of the Samaritans and all that pertains to them. In your humility, you asked if I would present you with all that I have to say on your words. However, dear friend, time is short, and your printer is demanding. How can I carefully look over and plumb the depths of your work with all the research that your 'pleasant garden' requires [and respond in time]? Therefore, I thought that it would be sufficient for me to present you with all that I have already written (in Italian, for my Grammar of Hebrew, which has yet to be printed) regarding the Samaritan or Old Hebrew script, and on the very old debate about whether the Hebrew script was changed or not. Without elaborating on the matters well known, I will add to that which the researchers have already stated, that if the script was not changed, then it is incomprehensible on what grounds some of the Mishnaic and Talmudic sages would say, from their own minds, such a strange opinion as this, to say that the script with which we write Holy Scriptures is not the original which the Prophets used. Quite the contrary, if the script truly was changed, and some of those sages denied it, we can understand why they would say it: to remove a stumbling block before the masses, for if our Torah is written in a different script from the one Moshe wrote in, this would be bizarre to the weak minded.
However, this proof is external, meaning that it relies on the testimony of the Mishnaic and Talmudic sages. I have an internal proof, from the Holy Scriptures themselves. In my researches, plumbing the depths of our Prophets and Sages, using the critical method, which seeks the truth alone, [this method] not appealing to the old [i.e., traditional Jews] and also not popular among the new [i.e., the Reform Jews], I looked all over the Bible (specifically in the Prophets and Hagiographa, which is not known to them, due to their excess love for the Torah) and found certain words which are errors due to the incompetence of the scribes who copied the books. I did not rush to disclose my findings to the public, because I know about the challenge which such critical research poses, and the many errors which are easy to make. Many scholars and so-called scholars, both uncircumcised and circumcised, boast that they make emendations, but they make errors. In many biblical passages I found what I myself thought was a scribal error, but after days and years I changed my mind and saw that the books' reading was true and correct. With all this, a small bit of the readings which I established in the texts still seem to me correct (now, as a 50 year old man, and after I have passed the passion of my youth) and sustained, above all doubt. Now, of some of these, I discovered that the mistakes happened through the similar appearance of letters, but not in our Hebrew script, but in the Samaritan script.
See how different is the appearance of a yud and a tzade in our Hebrew script (ketav ashuri), but it is the opposite in the Samaritan script, the two letters are almost identical. In Isaiah (11:15) we find: וְהֵנִיף יָדוֹ עַל-הַנָּהָר בַּעְיָם רוּחוֹ (and with His scorching wind will He shake His hand over the River). The root עים is neither Hebrew, nor one of its cognate languages. Therefore it seems to me that Isaiah did not write בעים, but בּעֹצֶם. I wrote this in my notes to Isaiah which I sent the scholar Rosenmueller, alav ha-shalom, and he printed in his 1835 book. Gesenius, in his W?rterbuch, explained עים (following Rabbi Jonah [ibn Janach]) from אָיֹם, but he reversed himself in his great Lexicon, and he took this explanation from me, and wrote that it seems that be-ayam ought to be emended to be-otzem, due to the graphic similarity between the yud and tzade in the Samaritan and other early Near Eastern scripts. 
 If someone says, maybe Gesenius did not see what you wrote and came up with it independently, much the same way you yourself, [Shadal], in your youth derived "tanur" from "aton nora" without seeing Gesenius - the response is, I have a Latin letter from Rosenmueller dated 24 April 1835, and he wrote this: "Gesenius reviewed all the pages, including your notes, and approved of them." This is not the only thing which Gesenius took from me [Shadal gives three more examples, and the places they can be found in Gesenius' writings - S.].
Also the aleph and tav are of similar appearance in the Samaritan alphabet, and from this we can understand what we find in Jeremiah 3:8, " וָאֵרֶא, כִּי עַל-כָּל-אֹדוֹת אֲשֶׁר נִאֲפָה מְשֻׁבָה יִשְׂרָאֵל, שִׁלַּחְתִּיהָ, וָאֶתֵּן אֶת-סֵפֶר כְּרִיתֻתֶיהָ אֵלֶיהָ; וְלֹא יָרְאָה בֹּגֵדָה יְהוּדָה, אֲחוֹתָהּ--וַתֵּלֶךְ, וַתִּזֶן גַּם-הִיא," "And I saw, when, forasmuch as backsliding Israel had committed adultery, I had put her away and given her a bill of divorcement, that yet treacherous Judah her sister feared not; but she also went and played the harlot." There is no doubt that Jeremiah did not write "וָאֵרֶא," "And I saw," but ותרא, "And she saw." The opposite (e.g., a tav replacing a proper aleph) occurs in 1 Samuel 24:11[sic; it's actually 10]: "וְאָמַר לַהֲרָגְךָ, וַתָּחָס עָלֶיךָ," "and some bade me kill thee; but mine eye spared thee." But its true reading is "."
Next follows quite a few other example, which I will return to and translate, but in the meantime, the two (one and a half, actually) above will suffice.
Returning to our subject, that the scribal errors we mentioned arose, without a doubt, because of the graphic similarity of letters [only] in the Samaritan alphabet, is in my view a faithful witness that the script changed and that our books were not originally written in our Ashuri script, but in the one which remained in use among the Samaritans. It is true that changing the script, and writing the holy books in a new script, not previously used by the Prophets for their books, does seem extremely odd. Not for nothing was the matter difficult to accept for many Jewish scholars and non-Jewish ones, so it seemed to them false, and they accepted the wrong opinion [i.e., that Ashuri was older]. But all this is because they didn't understand the reason, they merely heard the idea that the Jews changed the script, but lacked any idea about why, until they were left with the wrong view, that it never happened. If they had known the reason, and the circumstances which caused the Jewish sages to change the script, they would have been able to accept it, and would actually have thanked their predecessors [i.e., the sages, for changing it]. For it is known that the Samaritans tampered with their Torah and introduced many changes into it, large and small. This thing was a stumbling block for the simple Jews, because the Samaritans could, for example, point to what is written in their Torah at the end of the Ten Commandments, "And it will be when the Lord, your God, will bring you to the land of Canaan, which you have come to inherit, and you will establish large stone monuments and write this song upon them, etc. and when you will cross the Jordan you should establish these stones which I command you this day on Mt. Gerizim and build their an altar, etc. - from here is proof to say that their Temple [on Mt. Gerizim] was the spot chosen by God, and not the Temple in Jerusalem. So because of such changes by the Samaritans, the Jewish sages were smart and figured out a way to stop this problem and make a clear, lasting change between our proper books and their improper ones. They found no greater change than to write our scrolls in another script, so that even a simple person could see a Torah of a Samaritan and discern immediately that it is unfit.
This reason for the change of script was hypothesized by my beloved son Ohev Ger, the Lord keep and strengthen him. It is possible that this was what was intended by Jerome on Ezra (from his version of the Chronicon by Eusebius): "[Ezra] collected the holy Scripture, that they might not be mingled with the Samaritans, [and] changed the Jewish letters." [I reject] the understanding of this passage in Eusebius by Rabbi Azariah, that the script was changed in order to prevent the physical mixing of the Jews and Samaritans, but in order that the Torahs should not mix! - as he wrote, "divinas scripturas"
Actually, the change in the script did not occur in the days of Ezra, but later, for we find also in the book of Ezra and Chronicles scribal errors which are due to the similarity of lettes in the Samaritan script. Furthermore, when they changed the script they only prohibited its use for Scriptures, but they still used it for other writing (like the rabbis said, it was left for the plain folk). This is the cause of why we find coins from the Hasmonean era in the Samaritan script. In those times there were two Jewish scripts, one used for secular and one for holy writing. In the end the holy script prevailed, and the earlier script which was left for plain folk, was also abandoned, and remained in use among the Samaritans only.
Now we will discuss the names which the Samaritan script was known by in earlier times. In the Talmud we find it called Ktav Ivri, and also the Samaritans themselves called it Ktav Ivri, for they called our script Ktav Ezra; see their letter to Scaliger of the year 5349 (1589), which was printed in the book Repertorium fur biblische und Morgendlaendische Litteratur vol. 13 [pp. 257 - &c.]. Now, Rashi to Sanhedrin 21 explained "Ktav Ivri" as "of the people who dwelled over the river [i.e., Euphrates]." This explanation is justified on account of Sabbath 115 and Megillah 18, which refer to Coptic, Ivrit, Elamit, Medite, and Greek, and the intention there is to foreign languages. But how could this explanation pertain to the script in which the Torah was given, which was the ancient Jewish script, similar to the Phoenician script used by the people of Tyre and Sidon? Perhaps Rashi believed that the Samaritan script truly came from over the river, and was used in Eretz Yisrael in the time of Abraham, and from their it came to Israel, only he did not know (and it was impossible for him to know) that also the people of Tyre and Sidon used this script. And when I looked into it, and realized that Ktav Ivri [in this Talmudic text] did not mean a script used in the Land of Israel, and this was at the beginning of the Second Temple era, when Israel was reigned by the Persians. The Persians, who dwelled in the east, called the land of Israel and her environs to the west, "Ever Nahara" (Ezra 4, 5, 6, 7). From the expression of the king and the nobles, the Jews themselves, as well as the Samaritans, began calling their script by the name Ktav Ivri; note that the expression "ever ha-nahar" doesn't refer to any one side of the river. It's primary meaning is either side of the river, and depends upon the perspective of the speaker or listener. (To learn more in depth about "ever" see Gesenius' Thesaurus p. 986 and also what I wrote in Hamishtadel at the beginning of Deuteronomy) After the dissolution of the Persian Empire, the term "Ivri" returned slowly but surely to its original meaning, Aram Naharayim (hence the Talmudic list, Ivrit, Elamit, Medit) and the word "Ivri" as referring to Israel was from then only used in the phrase "eved Ivri" (for so it is called in the Torah), and Ktav Ivri (for this was its name as it was used by the Samaritans, who actually used the script). For this reason R. Abraham de Balmes, R. Azariah de Rossi and others who did not call the Samaritan script "Ivri" but "Ktav Ever Hanahar" were being inexact.
Sanhedrin 22, we find Ktav Ivri called "Ro'etz," and in Yerushalmi Megillah (first chapter) we find it called "Ra'atz" (i.e., without the vav). The scholar R. Moses Landau writes in his book Geist und Sprache, p. 104, that Ra'atz is like La'az. However, the word "la'az" was well known and used constantly in the language of the Mishnah and Talmud, so who could believe that it was mistakenly changed to ra'atz? Or to say, as a few scholars do, that the idea of ra'atz means a broken script (Fractur) is impossible, since the root of ra'atz doesn't mean broken in scriputral Hebrew, but only in the Hebrew language of the Mishnah and Talmud. When I looked into it, this is what I concluded. Now, the Samaritans refer to our script as "Ktav Ezra Ha-arur", the Script of Ezra the Accursed, (see their letter in the aforementioned Repertorium 13 pg. 273). Therefore the Jews, to retaliate, also coined a term of opprobrium for their script, and took the name of Ezra, which they used in referring to ours, and changed the letters around, also exchanging the letter zayin for a tzade, and came up with the term ra etz, intending "breaking." What is this like? Like Bar Kokhba, whose name they changed to Bar Koziva, or like Evangelion, which they changed to Even Gilyon - even though the terms "kazav" and "aven" are atypical for Mishnaic language, and are only used in Biblical Hebrew. [i.e., so it does mean "Broken" after all, and a clever inversion of "Ktav Ezra"]
When the Talmud asked, "What is Ktav Ivri?" Rav Hisda replied, "Ktav Livuna'ah." Many think this is one of the names for Ktav Ivri (including Gesenius). To me it seems that as the Samaritans lived in Israel, and not in Babylonia, and Ktav Ivri was unknown in Babylonia, so when they asked Rav Hisda "what are the hedyotot" he answered "the Samaritans." Then they asked him, "What is Ktav Ivri" but Rav Hisda did not know to answer "the Samaritan script," since he was unfamiliar with it. So he answered "Ktav Livuna'ah," which did not mean exclusively the Samaritan script, and it must have been a script known at the time in Babylonia, and [perhaps] it was somewhat similar to the Samaritan. And truly these writings are found in the ruins of Babylon and Nineveh on bricks. Some of these [=cuneiform] slightly resemble the Phoenician and Samaritan (see Kopp "Bilder und Schriften" II 152, 154) and Layard in "Nineveh" (Paris 1850) p. 173). R. Moses Landau in his book Ma'archei Lashon (p. 875) explained the word "Livuna'ah" from the term "levenah," (brick), but this is impossible. First, because of the vav after the beit, as it is written in the earlier printed editions, as well as my old manuscript of the Aruch, under the entry Ktav. The second reason is that the bricks [=tablets] in Babylon are not at all similar to the Samaritan, most are written in cuneiform, only the tiniest fraction are alphabetic. So I say that the term Livuna'ah does not refer to the Samaritan alphabet, but another script, and the true meaning of it is not possible for us to determine.
After this follows several pages on the poetic language of the Samaritans.
This is sufficient because of the lack of time. You my dear lerned friend, rejoice in your work, and rejoice all who love Torah and her aids. Peace to you and yours, signed Padua 9 Sivan 5611, your friend Shadal.