You will need a BIG wire to the "ign" terminal on the distributor cap, all the way from the ignition switch to the distributor- - - - -12 gauge minimum, and 10 would be better. Most likely, the wire from the switch is around a 16 GA or smaller, and it might possibly be a nickel/chrome resistance wire that drops voltage like a ballast resistor used to. I don't remember what year GM started using the nichrome wire, but it was somewhere in the late 1960's I believe. The HEI coil needs a lot of current, especially on a cold start.
Jerry
