The "usual culprits" with overcharge/ over voltage is this:
1...Some rebuilt alternators are incorrectly assembled with one brush/ field connection grounded
2...Rarely, the VR goes bad OR IS NOT GROUNDED
3...More commonly is VOLTAGE DROP. This can happen either on the ground side (VR MUST see a good connection back to battery)
..................OR.............drop in the ignition "run" circuit.
You can check for drop by turning the key to "run" with engine off. Connect your meter to the blue alternator field connection without disconnecting it from the alternator. Stab the other probe into battery + post. You should read very little, the less the better. If you read more than about .3V (3/10 of one volt) you have a problem.
The path and trouble areas are the bulkhead connector, the ignition switch and connector
If you cannot find or fix it, add a relay on the "run" line. Cut the "run" line coming into the engine bay, use the end coming through the bulhkhead connector to trigger the relay, and feed the relay contacts through a fuse/ breaker off your starter relay "big stud." Connect the engine bay end of the cut "run" line to the switched contact