pic: Simple single reduction duel CIM gearbox

[Steve Kaneb]

Why do you have the plates extending past the sides of the CIM casings? You would have to change the pocketing, but if you lop off those spare centimeters, you'll save some weight, space, and raw material.
In addition, you can probably get away with making 2 identical plates, even with the holes for the CIM screws. I would rotate the CIMs 90°, to make the symmetrical pocketing easier. Having swappable plates would aid greatly in manufacturing and would reduce the number of spares needed (not that these sorts of things break often).