drag Specialties 2112-0780.
says for Big Twin 70-75.

i know there is no reliable test for regulators, but for what it’s worth I poked where the power wire came out to the ring terminal at the end, and got about 1.2ohm resistance. I thought maybe there was a short in the wire preventing it from supplying juice to the battery.

Speaking of battery, I am running an agm style. It is also Drag Specialties, High Performance 310 cca for shovelhead battery tray.