Some progress today! I received the reduction gear and shaft yesterday.

I used the original gear on the new shaft, so I have a starter motor reduction gear if anybody wants it. It is currently a cat toy.

While I was installing the stator cover I had my latest 'not so proud of myself' moment. I was putting the final hand torque on the last new allen bolt and I felt the threads let go. Sure enough:

Fortunately I got really lucky. I was able to run a tap into the existing threads and cut a few more into the case. One of the old JIS screws was just a couple of threads longer than the allen bolt and I was able to use it instead. Crisis (and helicoil) averted.
So the next step is going to be getting the kickstand back on the frame, put the engine back in, and get the wheels with existing tires on so I've got a roller. From there I'll mount handlebars and do the brakes/suspension, and then start getting the chassis and electrical sorted out.