If your 6 volt system is strong and in working order there is no reason to change a stock car. For performance in a modern V8 yeah, you gotta go to 12 volts. My stock straight 8 1950 Packard has a 875 CCA 6 volt Interstate battery- that's equal to my 96 Eldorado's! A new starter will spin fast like it should on your car. The generator is a downside if you drive a lot. Lots of short trips= many start ups- never allows the generator to replace what the starts took out and then you have a low battery. If you don't want to mess with changing to 12 volt bulbs and fiddling with 12v to 6v voltage reducers to run instruments and such, just get a 6 volt alternator. Almost evryone in So. California with either rod or original stocker uses an alternator in place of a generator. This goes for old 12 volt systems originally using generators too.

My 6v Delco generator put out 35 amps and a 6v alterntor will put out 65 amps. With a very powerful battery like I got, I have absolutely no problems with weak lights at night. If you do lots of battery draining stuff you can just charge it up later but never have to worry about draining it completely at the time.