can be found here with a follow up from the Noda B' Yehuda's son.
The letter is really interesting and I hope to get back to it.
(Would appreciate if anyone can tell me if the letter has been discussed anywhere else?)
During the period he was rabbi in Holesov he became friendly with a Christian scholar. In the library of the academy in Leipzig there is a holograph of a Hebrew letter dated Feb. 3, 1660, which Shabbetai wrote "to him whom I love as myself, the philosopher magister Valentino Wiedreich." Shabbetai informs him that he has sent him the book of Elijah Baḥur and asks him to keep in touch with him (Bikkurei ha-Ittim, 10 (1829), 43–44).