Voltage Regulator Question / Pertronix

I don't recommend either of the voltage regulators you linked. "Duralast" is garbage, and I don't trust namenlosen generische nachbau components such as the eBay item.

Best voltage regulator you can get is NAPA Echlin VR-1001 or Standard/BlueStreak VR-128. The VR-1001 can be had overseas through this company.

See also here for advice on how to smooth out a jumpy ammeter needle. You may wind up separating the circuits that go to the ignition and to the voltage regulator's "IGN" terminal, by installing an ignition feed relay.