Voltage regulator problem with 1968 Dart

You for sure have someting wong VERY first thing I'd look at is a ground between the VR and field and or grounded field

I assume? you are still using the older style single terminal field alternator?

The older system has one field terminal and the remaining brush is grounded. So if you check resistance from the field terminal to the case, it will be quite low resistance, BUT NOT zero or full short. It is VERY common on isolated field alternators to find one field terminal grounded, that should not be

Next disconnect the green field wire from the regulator and from the VR. It should be zero resistance from one end to the other but open to ground. Believe it or not, we had a member here with one grounded--shorted, to ground.