do you not yet understand that this is another lie from the Samech”Mem? There is no such letter. If there was such a letter, certainly it would be known to Rav Landau shlit”a.
All of this is obvious if you have Torah. Rav Chaim ztz”l was not a kofer. Rav Povarsky shlit”a is not a kofer. All this is the same old tricks of the tziyonim, maskilim, etc. etc. back to Erev Rav at the Egel.
Again, to be absolutely clear: the Torah is what we Jews keep and if any Gadol b”Torah would, chas v’shulem, veer from it and tell Jews to endorse Z or J or Sh”tz or any other moshiach sheker, HE would be problem and we Jews would reject him and his Zionist-like teachings.