I could be wrong but what I think powermaster is doing is using a starter made for something else and it comes with the larger gear, and to make it work they offset the gear over some, hard to see but if you measure the 289 powermaster two bolt mount to see if the uni clock registry is exactly centered with the starter hole registry, I do not think that it is. If the powermaster 289 starter gear teeth will mesh correctly with a 289 flywheel it will mesh with the 200 flywheel ring gear if it is located correctly as the 289-157 and 164 and the 200 9'' flywheel, ring gear teeth that I measured are the same.
Of course the forward and back spacing of the starter gear needs to be right, too close it could hit and also could bottom out and not let the contacts fully close to start turning, to far away and the tooth engagement will be poor. I am sure what you are doing will work it just needs some tweaks somewhere.
I am sure that you are frustrated how it is going, if it was easy there would be one already made.
