Proportional type is impossible with a typewriter. So is the centering that they did. Also the use of a lowercase 'L' for a one, which is just a way to trick MS Word into not superscripting '1st'. There is more evidence here of forgery than their was for murder at the OJ trail.
Sorry, but you are not correct. The IBM Executive model, which was in common use during the 1970s, was capable of all of these things. It was famous for having proportional typing capabilities. Centering was as simple as setting a tab stop and using the correct keys to backspace half of the line length.
Now, would anyone go to this trouble for a memo? I doubt it. And I do think the docs are forged. But let's all stay clear on the real evidence, and not end up falling into a trap here.
No need to "trick" MS Word into not doing the automatic superscript -- you can just turn off that option. Though I seriously doubt that the amateur who produced these would know how to do that. Tools -- AutoCorrect -- "AutoFormat as you Type" tab - uncheck "Ordinals (1st) with superscript".
Actually, there were old typewriters that lacked the numeral 1, and you had to use a lower case ell. But, IIRC, the high-end IBM's did not give you that kind of problem!