The supers don’t use a crystal, they use a potentiometer wraped with enamled wire. I did replace the pcb’s on several. You loose the higher torque characteristics when you loose the super pcb, but you can get it all back and more with the mosfet mod.
I’m actually interested in this idea myself, but haven’t really come up with any good ideas. I did see someone do this type of mod before though. They took a bit steering compartment, hacked it off and replaced the pullbacks front with the bits front. He said it worked pretty good. I don’t think it really gave him any speed increase though.