A woman on another thread writes that she used to type theses in the 1970's to earn college money, on a IBM Selectric, and that she would swap out the font ball to type smaller font superscripts, somehow rotate the ball only half a space.
But IMB Selectrics don't have proportional spacing. This type on these memos does. It might have been done on an IBM Executive, which does have proportional spacing, but you can't swap the fonts to get smaller superscripts.