Charging issues on a ‘64 Valiant...

If you have an alternator with both horizontal and vertical brushes in plastic holders, then you can replace the parts and convert the wiring so it works with that type of regulator. Or you still have the option of grounding one and using a positive controlling regulator.
I posted a crib sheet for the replacement brushes and holders here:
Alternator repair, a little show and tell.

If your alternator is a later 'revised' squareback, those use different brush holders.