[Alex.Norton]

There is a retaining feature on the inside of the frame. The lexan on the top and botton of the cross supports would be pot riveted to the box beam keeping the side pieces from moving inward.

Any manipulators or other mehcanism would mount to the black supports because the side would be able to come off. In terms of the gearbox, hey why improve on something that aint broke. Its only partially custom (The side plates would be custom) but still sleek and easy to replace if broken. Of course unlike your design it isn't a shifting transmition.