I believe with the IBM Selectric, the balls used could be any font. Replace the Selectric ball, replace the font. I used to have to do this to type letters in Spanish and French.
In looking at the font, it doesn't seem to be one that I wouldn't have used back then. Sorry but very few items were actually monospace with the Selectric. An old-style typewriter would be a different story.
IBM never made a Selectric I or II with a proportional font ball, period. Only the IBM Executive had proportional spacing for characters. The IBM Selectrics only came with many varied but in the end, MONOSPACED characters.
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