Classic/Antique Car Repair: 6 volt vs 12 volt, electric fuel pump, autobobile

Question
I own a 1938 Pontiac Sport Coupe 6 cylinder. What are the dangers of using a 12 volt battery to start the automobile vs a 6 volt battery.  I planed on using a relay to start the automobile with 12 volts and switch back to 6 volt to operate the automobile. It takes a lot of cranking to start the autobobile with the 6 volt battery. I am running an electric fuel pump for the first 10 seconds prior to starting the automobile.
Thanks,
William

Answer
There was a company around a dozen or so years ago that manufactured a battery system like you describe. I had one in a 41 Caddie that I bought and it worked fairly well. However when it came time to sell the car that system turned off a few buyers. So, I hauled the starter out, did a careful rebuild including new bushings that I hand fitted, and the car started fine, and sold for the price that I wanted. What you describe will work. The new fuel injected cars with computer control run the fuel pump from one to two seconds on key on and don't turn the pump back on till the engine is running.
Brad