For the PSU: Some people use light bulbs, but they are relatively fragile and I don't like getting broken glass in my skin when I reach into my toolbox.
Maybe nothing needs to be loaded - there could be some sort of other turn on mechanism. Hard to say though...
For the shimming: There should be no side to side motion - that's probably what's causing your problem. The pinion should be fully meshed into the ring with NO play, but make sure it still runs freely, especially after you get the case together.