The only change you need to make for the generator to charge a 12v batter is reset the regulator. There are three "relays" inside the housing, a cutout, a current regulator, and a voltage regulator. There will be a screw adjustment or a tab holding the spring on the voltage regulator that you can adjust to set the voltage to just about anything within reason and 14.3 or so for charging should be no problem. All the wires stay the same. With 12v on a 6v system, all the wires are oversized and will carry things more easily, no need to change them.
A web search for "voltage regulator adjustment Chevrolet 6v" hits about 6 threads on this forum. Those instructions work to reset for 12v too.
