Dave the Machinist brought over the finished coupler late Friday afternoon and he's clearly gone above and beyond. As he'd suggested, he machined out the center so a bolt could be inserted in the threaded hole in the motor shaft to provide an additional attachment to secure the coupler to the motor beyond the heat shrink.
The splined portion of the motor shaft will be fully seated in the remaining splines of the coupler.
Rather than trust a stock washer, Dave machined a custom washer from high strength steel with about a 3/16" thickness and a perfect fit for the recess.
Fitted with a grade eight bolt and lots of thread locker, the coupler's not going anywhere.
Finally, Dave machined a spacer to position the coupler precisely on the shaft and maintain the narrow clearance between the coupler and the static motor end plate.
Dave has an oven in his shop that will take care of heating the coupler for the shrink fit, so Robert will strip the accessories and mounts from the motor and wheel it over to Dave's shop next door for final fitting.