IBM offered proportional spacing on their Executive model, starting in 1944 (it was developed in 1941, but IBM's activities supporting the war effort delayed its introduction). This illustration is from
an ad in the fifties:
It was not until a few days before the advent of the Won that IBM introduced the Selectric (changeable bouncing golfball type element).
In 1968, I recall using a machine (can't recall if it was IBM or Wang or somebody else) that did kerning. It had a small memory that would buffer characters as you typed. When it had enough characters to form a line, it would type the line using a a Mylar ribbon all nicely kerned and justified. The college newspaper used it to crank out camera ready copy
for offset printing.
The IBM Composer was IBM’s attempt to get into the typestting market in the early 70s. It was based on the Selectric, and had a magnetic card for storage and a composing unit about twice the size of today’s desktop computer box. Typesetting was done on the Selectric, recorded on the card, then played back using the Composer unit running the Selectric. The second pass through of the work could produce justified copy, or ragged left, ragged right, or centered type. Type sizes were adjustable up to about 14 or 16 pt, and there was limited kerning. If I remember correctly, it was also capable of setting inferiors and superiors, so it could be used for some mathematical typesetting.