In addition to the "Selectric Composer," the IBM Executive Model typewriters used proportional spacing. These predate the Selectric, do not have "the ball," and have a moving carriage.
I am looking for keyboard layouts for the IBM Executive ...
On the Executive, you could optionally have removable type-bars. This is somewhat like later Smith-Corona portables which have removable type-slugs on the two outermost type-bars, with corresponding changeable keytop caps. In this case, though, it's the whole type-bar.
http://www.geocities.com/wbd641/TypeManuals2.html
I'm now looking for type-bar and key options. The whole set of relevant superscripts would be "st" "nd" "rd" and "th." Remember, this typewriter DOES provide proportional spacing.
"On the Executive, you could optionally have removable type-bars. "
Yup. This feature allowed IBM to offer the Executive in various languages, and in special versions for specialized fields.
If I remember correctly, all the type bars on the Executive could be exchanged for others, which made the machine very flexible. IBM was very good at that sort of thing.
I do know that the one I used had characters for superscript "th" and "st" It probably also had "rd" and "nd". I suspect that was a fairly common option, since it would help documents have that typeset look.
The Executive was a pretty common unit, particularly in legal offices, small publications, etc. My hometown church had one for the secretary. She used it to create the bulletins.