>>So the memo could not have been made with a typewriter.
It could not have been made with MY IBM Selectric using the ordinary Prestige Elite 12 pitch wheel. I don't have a left and right apostrophe, only straight. But maybe a fancier machine, although not in your ordinary Texas Air National Guard office? Maybe the guy was part time and worked full time in a law office or was a business executive?
I have calls in to my old boss, who taught me printing and collects typewriters and old typesetting machines, and my mother, who was a typesetter.
I think this is a question best answered by an expert, maybe someone at IBM, or someone with a specialty in document examination.
But I did read that one expert has already stated that the "4" has a closed top and no "foot" which is ONLY found in Times New Roman, and that Times New Roman is found ONLY on computers.
The print pressure is to even also. Mechanical typewriter print varied because of the varying pressure used to tape the letters.