Sam,

The swap to 12 volts would probably be MUCH less painless (and not expensive either) than messing with some bizarre method of splitting various systems up.

The standard switch would always have to include the charging system. The original 6 volt starter will work fine on 12 volts and the only other issues other than changing several bulbs would be the heater motor and fuel gauge.

The Runtz type resistor would handle the fuel gauge and the HD voltage reducer would work on the heater motor.

This is the whole enchilada...you're done! You now have a conventional, working system. Pretty painless, huh!

Stuart