Good question. I once tried this, and it won't work. The starter drive from a 12 volt starter won't fit on a 6v armature and vice versa.
The footmash 6v starters work fine on 12 volts, but the 6v solenoid starters (sedans) don't like 12v. My '54 ate the teeth off the ring gear quick-like on 12v. :o So I swapped to the '60 model setup and no probs.
