Wow! You have really put a great deal of thought and effort into this. Thanks muy mucho!
FWIW, another approach to loosening it if needed would be a 0.160" diameter hole in the periphery of the exterior, perpendicular to the axis; in the same manner as the chuck and its scrolling ring. That would have allowed a standard Sherline chuck tommy bar to be used to loosen it if needed.
It sounds like round will be harder to overtighten by hand, so that's a good plan!