I welcome the advice, Thanks.
With the exception of the shaft length I'm having a pretty successful conversion effort. Muffler fits. Mounting and clearances are good...
Did a check yesterday on the depth/strength of the prop hub area. Going to counterbore into the prop enough to drop in a prop washer and a GP 5/16-24 nut/spinner adapter. Still leaves enough meat on the prop hub for strength and balance.