Less worries going backwards than forwards, Phil. If you send 12v to something that wants 6v, you've got worries. Send 6v to something that wants 12v, and it will work poorly or not at all, but won't fry.

Look for a PO-installed dropping resistor on the fuel gauge. I believe that's the only electric gauge on a PV.

Hook 6v to the motors (wiper and blower) and see if they work too slowly. I suspect they'll be fine - especially since a resto of this type will only be a fair-weather driver anyhow.

Of course you will need a 6v generator. I may be able to find you one if you can't find your own.

Lucky it is a very simple car, electrically speaking.