Mission accomplished using
@cyclops222 method in post #4 above. I had some threaded rods left over from an old project years ago that worked perfectly. Only issue was that I couldn't get the exact torque on the bolts (got the factory ones from Mercruiser when I ordered the new starter). Service manual calls for 30 foot pounds on each one, but closest I could get was about 20. Just couldn't get enough leverage in such a tight space.
Amazing how much faster she cranks now!
About the PMGR starter, I can't find one with the same mounting pattern as the one I have now. Definitely nothing even close at NAPA! Besides, I wouldn't even consider an automotive starter. Anyone have a source for this?
Thanks again to you guys!