You said you have the engine grounded to the k frame. For my 2 cents I would run a ground strap from each head to the fire wall because k frame is not one of the best places. Most mopars run a ground from the engine to the frame rail and the fire wall
Might try that tomorrow, going to run the pos. straight from the MSD box back to batt. as well. We changed the carb tonight and still had the same results.