Alternator surging

If your alternator has two small gauge wires, then in 69, it should have had an electro mechanical regulator. Those have points in them, which play a lil tune on the dash gauge, which is normal until the battery comes up to charge. Eventually with a fully charged battery, they settle down.

If your alternator has only ONE small gauge wire on it, then it should be matched to go with an electronic regulator. These guys switch so fast between charge and discharge that you cannot really see the flicker on the sloooow Mopar gauges.

However a two wire alternator, can be converted to a one-wire just by grounding either brush, and then you can run an electronic regulator.
But you cannot go the other way, obviously, without taking it apart and modifying it.

If your electro-mechanical regulator never settles down, that is reason to suspect a problem.