I've made it to the correspondence, which is in the C's of the personal files. The correspondence takes up over half a filing cabinet on its own.
I've come across a letter written to Ong in Dec. 1967 in which the author writes that he's worried that because of The Presence of the Word Ong will be attacked for totalizing, but that these attacks won't really be about totalizing but will instead be attacks on Catholicism with Ong, McLuhan, and others as the supposed targets. This notion seems strange -- or would seem strange -- except that I've run across enough of it already in Ong's files (occasional letters, a readers' report for Ramus, Method, and the Decay of Dialogue that was clearly responding not to the book but to the book being authored by a Jesuit, etc.).
Ong replied with the note that he hopes he's included enough demurs throughout and that the "last paragraph of the book enters a final explicit disclaimer of totalism."
I mention all this because it's indicative of Ong's own method and how he is misread. He qualified his writings, but they were often missed or ignored.