ballast resistor location if there is one

Ballast resistors were a mopar thing , see if there's a condenser under the distributor cap that may be it , look for good motor to chassis ground . Probably spark/ignition because the fuel is stored in the carb .

The hot wire going to the distributor is a resistance wire on that era GM. Your symptom sounds like a bad ignition switch to me. To remove the ignition switch, put the key in the ignition. Insert a paperclip in the little hole in the front of the lock cylinder. Push the key in and turn it counterclockwise to the accessory position. With the paperclip inserted you can turn the lock cylinder past the accessory position and pull it straight out. Now unscrew the bezel holding the ignition switch to the dash. Working under the dash pull the ignition switch out from behind the dash with the wiring attached. Release the plug from the ignition switch, use a flat blade screwdriver in the slots on the sides of the plug. Once you get the new ignition switch installed, insert the lock cylinder into the switch just like you removed it but without the paperclip. The lock cylinder will lock into the ignition switch. Hope that helps! Jim