Retainer 2
Install the allen head screws. Snug them down, but DON'T OVER TIGHTEN. Maybe use a bit of light Loctite.
The screws really only serve a temporary purpose: to hold the spider hub & bearings in place w/in the bowl gear until the assembly is placed on the transmission output shaft, and bolted down.
Once this assembly is torqued to the transmission shaft, there's no where this "spacer washer" could possibly go.