HEI ignition troubles

RELAY: Using a relay in the "run" circuit is not at all a bad idea, except in this case you really did not go far enough. "The usual failure" in the "run" circuit, is that voltage drop in that circuit causes the voltage regulator to see low battery voltage, and this causes it to ramp up alternator output, thus actually causing an OVER voltage situation. When you get this sorted out, you should also tie the VR /field into the relay output