Have you considered a Tapper lock fly wheel?
Flywheel bore has been bored tapered:
Splined tapered wedge fits into flywheel bore:
As Flywheel is drawn up tapered wedge, assembled assembly becomes tight on Crankshaft:
Allen Machine Works
112 Overhill Dr.
Jonesborough, TN 37659-4346
I have no connection or financial investment with this firm:
I do know a "Tapper lock fly wheel" was the answer & cure for many 2 Cylinders.