Beltfed, do you have a picture of that alternative switch?
Craig's other option would be to fabricate a bracket at the transmission shift arm and shaft and mount a microswitch that closes, completeing the starting circuit, only when the shift arm is in the Park position.
I did that at the Lokar e-brake handle on my roadster to sound a buzzer when the e-brake is on to keep me from having a senior moment and driving off with the e-brake still on. Lokar sells a kit for that but to me it is way over priced so I made my own.
