2 6v batteries, tap off 6v for yer lites, gauges, heater, use the full 6v+6v for the v8, w/ a 12v starter and alternator - seems a lot easier to change the bulbs and put a dropping resistor in for the gauges and heater - can't imagine you'll make a V8 run on 6v, or find a 6v starter that'll fit it, + you'd need a 6v coil and 6v alternator [or generator

] - like GMC sez, why? :confused:
Bill