To 12 volt the '37 Chevy can I keep the 6 volt starter and generator and just change the coil and voltage reg with the 12 volt battery?
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1937 Chevrolet 2 door master deluxe sedan
1947 Cadillac 4 door series 62 sedan
1941 Chevrolet special deluxe 4 door sedan for sale

Nope. About the only thing you can keep is the starter. A 6 volt starter really wings an engine over when you apply 12 volts to it. You need to replace the generator. I'd use an alternator. You'll have to whip up a mounting bracket. All the bulbs, the coil. All the switches if they are in good condition, will be ok. Ditto, the gauges, but you will need to drop the voltage to them. See Ron Francis or some other wiring source for the parts to do this. it's not a bad job, really.
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Fred aka ZZFord or 33Highboy

On my '37 Plymouth, I kept the original starter, but switched the lights to 12 volts, threw in an alternator and a 12 volt coil. The gauges can stay original, but use caution with the fuel gauge. The simplest way to drop the voltage to a fuel gauge is to go to Radio Shack, and get one of those $12.95 3/6/9/12 adjustable voltage supplier that plugs into a cigarette lighter, the ones used to to power gameboys and stuff like that in a car. Cut off the big plug and use this line as input, set the voltage for 6 volts, and cut off the little plug and fasten the wires to the fuel gauge. Also check the polarity of the battery; mine had a positive ground when I got it. And definitely check the condition of those big thick cloth covered 6 volt wires. If they're cracked, trash them. If they're good, then they'll work with a 12 volt load, because when you double the voltage, you cut the amperage in half. Good luck...