Thanks- you were exactly right . There is a hole in the bracket that will allow access to the connection of the large and small crank. It was a walk in the park , once I saw the (4) machine screws that held the motor to the bracket. I had to drill a hole in the new small crank arm for the roll pin.This portion is complete. I assume that on start up of the game the cannon motor will run and the (2) switches will orient the cannon in its home position. I think there is a little bit of adjustment on the topside with (4) screws that attach the gun shaft assembly to the plate nut.
Maybe the diagram is missing in my manual. On page 2-32 the parts are listed for the U-gun Motor Bracket assemblies, but no diagram.