I am running an MSD box, EFI computer, big electric fuel pump and AC.

Plan A was a Powermaster 75A MOPAR case dual field alternator and flat pack alternator. It worked... barely. Dim lights at idle and just barely kept up when running at night (brights + AC).

Plan B is the 100A big case alternator from my '78 core engine (remanufactured) and flat pack 2 field regulator. Works great, plenty of output but heavy.

If your car is stock except the ignition, the above would be overkill. I understand the electronic ignitions don't like the old points type single field regulator but do get along with the electronic replacements. Your original single field setup with an electronic regulator (common parts store replacement) would work if you don't mind the normal OE dim lights at idle. Upgrade to a 60 or 75 amp 2 field unit would improve the situation. Wiring upgrade and bypass of the charge wire bulkhead connector is strongly recommended above 60 amps... and a good idea with a smaller alternator.

If you want to get away from the dim lights at idle situation completly, the Denso replacements are great. See Mancini. I couldn't use the big (120A) Denso as its not compatible with the AC pulley setup. I also couldn't use the 140A Powermaster adapted GM alternator as it hit my Ed heads. With iron heads it just might work.