Now to think of it I did install a new voltage regulator from the parts store last week. Factory one seemed fine just looked rough and I’m on a mission to clean up the engine bay. I’m gonna try putting the factory one back in and see what happens.
I would also take car to parts store and have them test the alt, especially for bad diodes. (free and easy)
My 67 would (while sitting at a light) wiggle the AMP meter. I had the alt tested and they reported bad diode. I replaced it and the wiggle is gone.
The diodes convert the AC from the alternator to a form of DC and if diodes are failing the DC is less DC which can result in a flicker etc.
BUT my bet is on the voltage regulator, especially if you did not notice it before the change but notice it now. If that is not the case and it happened before then I would focus on the alternator.