prewar engine help

Yes but that's what you deal with, with remanufactured parts. And for buying from 3 different parts places, they all probably get them from the same place. 

They are offset because the motor is offset to account for the thickness of the gears on the one side.  The offset in the fiber plate will allow the roller to be centered provided it is installed correctly.

EDIT read again, and see you mean the mounting tabs on the fiber are not lined up like the originals.  I've not noticed that issue on any  of mine, maybe double check the need to trim with a fit up.

If needed you could use a washer to ensure the wheel gear does not ride up on the motor side plate.  Keep in mind, you do want to make sure you have proper gear mesh/contact.  You do NOT want just the corner of the gears in mesh.  And, this is a big AND too... I have had to file down or trim that boss on wheels quite often to ensure the wheels where not too wide or out of gauge wide. 

I feel your pain Jim especially with the wheels. Most times ya don't need a shim but when dealing with compound geared motors SLS 11 gears, I don't see how you can avoid shims, otherwise you'll chew up teeth. I use flat steel thrust washers which my parts guy recommended.