[RC-Monster Mike]

You may want a couple more screws holding the diff. "only turns the dogbones" is true, but this means power and brakes for a heavy/large truck. You have until Thursday to address this! :).
Also, rather than spacing the entire motor mount, you could remove the material at the motor mount itself(where the screws go through) in stright lines (up and down), so the motor itself could slide upward or downward instead of the whole mount. This would be easier to adjust, as well as allow the flat section of the angled aluminum to rest flat on the chassis-more stable as well. :)