1964 Valiant

1964Val said
Regarding the alternator and regulator, Should I be looking for a grounded field regulator or switch out the voltage regulator to isolated (to match a new alternator)?

I personally like the simplicity of staying with the grounded field regulator.
Its a simpler system and I feel its easier to troubleshoot.
If you ever need a replacement you can just look up the regulator for a '64.
Finally if you can't find a grounded field alternator, its relatively easy to convert an isolated field alternator by grounding one brush.
Example of one way to do that in post #3 Identifying Chrysler Alternators (1960-1976)

1964Val said
The new wiring harnesses are OEM type from M&H

That will be for a grounded field alternator. PS. Save the oriignal harness for parts and reference in years to come.

1964Val said
I’ve been told that I will likely need a new ammeter, but that seems to be a “good luck” find in the short term. The current ammeter is pegged in the middle, but I recall it flickering slightly before I smelled burned wire. I caught a pic of the back of the ammeter as best I could, with some of the damage evident,

Middle position correct. That indicates the battery is neither charging nor discharging.

This is from a '75 Operator's manual, but I suspect a '64 is almost exactly the same