I'm going to assume it's a harley copy. No, there is no shim needed. Yes, the shaft, keyway cuts, circlip grooves are preset to length and use nothing at either side of that worm gear. So Bulletproof it does not gall the pump floating like that.
However, we have a circlip position and that is where we look at the circlip and see a cut and smooth side. If we look how that is one shaft, we need to float back and forth and so the cut sides are facing out. Why? So when the thrust happens, the cut side digs into the groove, not the round side about to roll out with one good thrust at it.
Make sense?