I think it's pretty clear that neither an ordinary IBM Selectric nor an ordinary IBM Executive could produce this copy.
I am still waiting for my old friend who teaches printing and collects typewriters to get home, my mother doesn't remember anything like this from her typesetting days.
OK, I found an IBM Composer and remember using one now. You had to type everything twice to make type come out justified. I guess you could have used it as a typewriter, but Gawd, why would you want to?
They don't have images of the fonts but the manual lists the special keys and it doesn't list a smaller "th" superscript.
http://www.ibmcomposer.org/SelComposer/Manual/toc.htm
Maybe they had the runaround that others have mentioned, turning the platen halfway and swapping for smaller font then swapping back, but why would anybody do that for an internal memo?
I realize the only way to prove it's impossible is find an old machine and try typing on it, or at least compare to Times New Roman and the typeface on the memos, which appear to be Times New Roman.