[asid61]

Looks very clean.
I like the use of thunderhex and circlips to retain shafts and use round bearings, but for the amount of manufacturing this requires you may want to use 1/2" bearings and shafts with ends rounded. It's a pretty simple lathe job that IME is comparable to an e-clip slot.
You could probably get away with only 4 standoffs, but for mounting purposes you could keep it like it is I guess.

I noticed on the plates your radii are pretty variable, with a 0.04 radius in one of the plates. Depending on the machine, this could make it take considerably longer to machine than using a single larger radius throughout, as a larger endmill can take off more material in general in a certain amount of time.

Overally a pretty sweet gearbox.
It looks like it fits very well into the back of your WCD.