[Ken Patton]

Theres some good advice on this thread, hope you are seriously considering what they said, rc_cola.

One item not yet covered - if you are going to use a sprocket on the output shaft to drive a chain drive, you should think about the shaft loads that will result from the chain when the motors are at full load and the wheels are stalled. The chain load can be pretty high for a drive with this output torque.

One other thing you might consider - the standoffs that you are using there look pretty skinny. Along with making sure you have adequate strength of the sideplates (as Greg already said), I would make sure you have enough contact area between the standoffs and the side plates.

Ken