Originally Posted by Rodney

There are going to be internal differences between the 15-91 and the 15s without potted motors due to the motor gear needing another gear inside the machine. I'm not sure of how easy it will be to swap parts back and forth.
I would say if you have a spoked handwheel on your machine already to keep it there. They're nicer to turn by hand than the smaller electric machine ones. I find myself using the handwheel a lot for fine detail type work.
Rodney