Alternator problem

I don't think your alternator problem has anything to do with the alternator, unless the battery is just "that dead"

The isolated field alternator you bought should work OK so far as a replacement --as cam64 said above. Just ground either of the field connectors and hook your existing regulator wire up to the second one.

It's POSSIBLE maybe even probable, that your problem is NOT the alternator at all. You may have problems with the bulkhead firewall connector, a loose connection somewhere, such as the rear of the ammeter, and all these cars have factory welded SPLICES in the main harness. These splices are subject to failurew