I think you got it. The "big" difference between grounded field and the 70/ later scheme........
The single field connection/ grounded field, the VR SENDS power to the field, so jumper power to the alternator field to test
The 70/ later the VR wire GROUNDS the field, as the other field terminal is supplied batt power.
See if you have power to the VR. See if there is any power going to the field. Disconnect "green" and feed power to the alternator field to test. if that works and the VR has power, must be bad VR
