Alternator/regulator upgrade

You may be jumping too soon. The readings you posted contradict each other. The ammeter should not be showing that much charge with that little battery voltage. Maybe the battery has a dead cell or is just wornout 'bad" or is nearly dead. Very first thing to do is try to charge the battery and have it load tested......but a real load tester, not some "pocket" instrument

Next thing I'd do is get it running and up on "fast idle" to simulate low-to medium cruise and RE check battery voltage and then measure voltage at the big output stud on the alternator. Maybe a big voltage drop in the harness is causing the low reading. Both the battery and the output stud should be within maybe a volt of each other

If you happen to have another "easily removed" known good 12v battery I'd swap that in and see if there is a difference

That alternator is basically a 70' and later Mopar incorrectly called "dual field." Correctly it is "isolated field. Someone like Powermaster has added an on board regulator to turn it into a functionally "one wire" alternator I believe.