[goatless]

That image has been very helpful for me in my wiring efforts, but either I'm not seeing it or it's missing the ballast resistor wired between the positive coil and the firewall (the 20 W/OR/PPL purple wire).

Might lead one to believe that in a points setup the coil always gets 12 volts as opposed to only when cranking the engine. I am assuming it's a points setup because of the yellow 20Y wire going from "R" on the solenoid to the positive side of the coil.

IIUC, the points can't handle 12 volts full-time, so the resistor reduces input to the coil to ~9 volts when the ignition is on, but when cranking, the "R" supplies 12 volts to help start the engine.