You'll find that the gas gauge is the only one to worry about. The AMP gauge doesn't care if it is 6v or 12v, and will work exactly the same on either.
Temp is mechanical, oil is mechanical and the light bulb replacements can be had from the parts store or radio shack. I ran a voltage reducer (Runtz, probably did not need it), on my gas gauge until the gauge went bad. You need to make sure the sending unit in the tank has the same ohm range as your gauge. Not a problem if you are using the original tank and sending unit. I've been told that the gas gauge will work on 12V, but I have not tried it and makes it makes no difference to me now that it is broken.
