I got the parts back from Tulsa's Aircraft Specialties.  See photos below. Nice folks and they expedited in one day once I called to ask for fast service.  For reference, grinding the knurled shaft was $75 including inspections prior and post work.   The brass worm wheel needed turning to a sloped specification and that was $50.  The replacement undersized spring was about $250.  I have to order some replacement bearings but those are $11 each at Spruce.     I'm hoping to test the adapter and starter on the bench using half voltage to make sure everything spins nicely before hoisting the engine to install the starter adapter.   The entire overhaul kit for hardware and bearings and gaskets is available from Niagara as is the grinding work.  If you were to overhaul/repair your own starter adapter (I'll post a youtube on the process) it is fairly simple to disassemble, check and acquire the work/parts needed once you see what is involved and have a source for this work and the parts.   My costs will be in the $400 range and my quoted costs were $1100-$1800 for an overhaul/repair and $3000+ for a TCM solution.  So far, I'm pleased with Niagara taking their unit back and for Aircraft Specialties in Tulsa for getting this work done so quickly.