pic: low profile 3 CIM gearbox

[Knufire]

Originally Posted by Chris is me

Regardless this approach is probably fine, just be careful to make sure the inner bearing is very carefully aligned. If bolt holes are the only thing constraining that bearing in place, that might get tricky to line up as you assemble the gearbox. Especially if you are running this with a third bearing in the drive tube / plate / whatever.

Considering you didn't pocket the plates at all, I might even go down to 3/16". That way, a bit of the bearing on the output shaft will stick through the plate and allow you to pilot the whole gearbox correctly. But then you'd need to put clearance holes as the 3/8" bearings would stick through as well. Always a tradeoff.