I checked this out with my "expert" (Google), and he came back with this link
http://www.ibmcomposer.org/SelComposer/description.htm(with pictures). In 1966, IBM began producing a version of the Selectric, the "Composer", that could do proportional spacing, but it appears to have been a high-end, professional model that wouldn't have been very commonly used.
Apparently, you had to type a line, record the number and the line's length separately by hand,
then re-type the line with the number and line length inputted into the typewriter. Basically, it looks like an extremely top of the line typewriter that an average person would not use, especially for a note to one's own file. I doubt most secretaries knew how to use that thing, let alone an Air Force officer. Check out the link for the pictures, that thing looks un-Godly complicated.
Thus, I still think the proportional spacing font indicates that these memos are forgeries. Perhaps some experts could weigh in?