Which generator do you have ? 1 has 2 ball bearings, the other has a bushing.
the original rear bearing for the 2 ball bearing generator was a 2 piece bearing and the outer race should have a spring to keep pressure on the bearing, most times it is replaced with a modern 1 piece bearing, that also should have a spring to dampen any movement. The ball bearing should fit tight on the armature shaft.
your end plate could be stuck with paint, or the locating tabs could just fit tight.
make notes on the location of the wires, pulling too much on the field wire can pull it out of the windings.
look inside the field housing for splatters of solder flung from where the wires are joined to the commutator. ( mine had this happen on the maiden voyage --i was told that resoldering would be a tempoary repair--40 years ago --and still working)
If your endplate has a bushing and it is tight you can leave it alone, but you do have to clean out the oil cup, and felt wick so the fresh oil gets to the bushing.
If you have to replace the bushing it can be threaded and a bolt used to remove it if you don't have a proper bushing remover.
if the ball bearing race stays in the end plate you can try tapping it on a wood block --lightly, or you can check the tool places for a small pilot bearing puller --that same size bearing is used for pilot bearing on many other cars. ( the original 2 piece bearing is often called a magneto bearing)
