If you plan on running the six volt alternator you would be better to go with a six volt battery. If you want to run eight volt that will give brighter lights and faster cranking. You would need to run the original generator with the Fun projects eight volt can style regulator. Bulb life would be shorter but bulbs are inexpensive enough that it wouldn't be of real concern to me. Don't get me wrong, I'm not recommending this. It seems that an eight volt battery would be harder to find when you needed a replacement. Good six volt batteries are getting expensive. The last one that I bought. at O'Reilly's was something like $89.00 it was the lowest cost six volt battery in town, it lasted about two months, They replaced it without question. the same thing has happened two more times in a row. There is not much that still uses six volt batteries anymore and it is hard to know how long the available six volt batteries have been held in stock on the shelf. I run our roadster on 12 volt with the original generator and use the Fun Projects can style twelve volt voltage regulator. This conversion requires the use of a resistor on the original coil or change the coil to a 3.0 OHM unit that is internally resisted and is readily available. The very mention of a twelve volt conversion upsets a lot of the guys here so I make no recommendations here about anything. I just state what I have done, how I did it and how I like it. I like the 12 volt conversion. Parts are readily available at reasonable prices. The only experience that I ever had with eight volt batteries was my dads old forties model civilian Jeep, It worked quiet well, the lights were very bright. We never had to replace the sealed beams for the years that we had it but it wasn't used for primary transportation. Its your choice.