This is what I did on my CB750 chopper, which is essentially the same get-up. I machined a plug for both sides, with one side having the o ring, and threaded so they could be screwed together. You have to machine them with enough meat so that you can thread to top in order to mount the cover. The cover mounts to the frame of the starter motor. I simply removed the gears on the starter shaft, since all they do is engage a gear on the crank. I'll have to check my 550 motor I have in storage, but I think I'm telling you correctly. I installed my electronics in my starter housing, except for the reg/rec.