starkweatherr,
The old, 6 volt physical wiring would be technically "twice" the required gauge for any 12 volt device, so if it's in good shape, it would certainly work for any 12 volt future plans.
If you stick in a 6 volt generator, you will need the corresponding regulator. Using the 12 volt version won't allow the system to charge.
I'm not clear on what you actually want to do with this truck. The options would be to go with the stock 6 volt system, which would include generator, regulator, gauges lamps and battery.
To swap to 12 volts, you would have to change to a 12 volt generator, regulator, battery, lamps and voltage reducer in front of any small motor or gauge that couldn't conveniently be changed to the higher voltage.
If you do the 12 volt swap, and you are not a purist, the alternator route is a good way to go.
You can utilize all the existing wiring if it is in OK condition. Some small changes would have to be made, but not a complete R&R by any means.
Does this mini-novel help answer your question?
Stuart
