I had to assemble an FT16D motor with a period arm supplied along with the parts. The problem here was that the arm was made for the earlier can with the blind bushing, rather than the later can with the rotating bushing, and there was very little tail shaft and no tail spacer... ack! First thing was to make the arm be able to space against something, so I installed a teflon washer to protect the tail end of the coils, and then installed a brass press-on tail spacer.
Supplied with the parts was a 6mm x 2mm bearing for the can, but with the can reamed out for the bearing and the bearing installed, there wasn't enough length to have the arm actually in the bearing. Before, I would have either had to figure out some weird way to handle this by hacking a piece of tubing or just sent everything back to the owner saying... "I gave it my best" 
Now, all I had to do was whip up an adapter with a collar on the outside of the can that protruded far enough insode the can to locate the arm in the bearing. It took some trial and error to get it to work, because there was no room for slop. It was either going to work or it wasn't. In the end, it did work and I could solder-in the adapter, and then epoxy the bearing into the adapter. The tail shaft was so short that, even with the arm fully seated, it doesn't ride all the way through the bearing... but it pretty much does!
Anyway, being able to figure a way out and then doing it is sooo nice!
