this is my second rimfire, if i remember correctly the first one did not have such a large collar over the shaft, if i recall correctly instead of the collar + set screw it was secured to the can via a circlip like the ones holding the shaft in gws style gearboxes. i suppose you could remove it if you were running the motor upside down, inside the firewall with a prop adaptor. wich would explain why the mounts need to be revised.