Not knowing the name of a part is an easy fix; check out tip # 39 at the link.
Even a $19.99 toaster comes with an operating manual. That 60+ year old tractor has more moving parts than your toaster. You need the manuals.
Re Harold's question......if it's an up & down movement, no problem. Sideways movement is always a problem.
The "square thing" is called the distributor cam. It sits on the shaft. If the bushings at the front & rear of the shaft are worn, the shaft moves. If the shaft moves, it effects point dwell. And that's a no-no.
You have three choices.
1. Buy a new distributor plate. It comes w/ the front bushing installed. And it will have a new insulator as well. (save the concave head brass screw from the old plate because new ones don't come w/ them) You will still need to buy & install the rear bushing.
2. Buy both bushings & take the distributor to a machine shop. While the bushings seldom require reaming to fit, some do. And that's more of an art than a skill.
3. Do it yourself. If you want to try it, make 100% sure the "tower" on the plate is firmly supported before you try to press out the old bushing & install the new one. Distort the tower & you will be buying a new plate.
And in case you're wondering:
Rear Bushing ID .863
Front Bushing ID .437
Shaft top .436
Shaft Bottom .863