1966 Plymouth Barracuda Help!

Your distributor wire should go to the negative post of the coil. As for the overheating issue I would suspect that you have a blown head gasket since you have pretty much done everythin else to prevent overheating. Have you checked the oil after running hot? Is there water in the oil? One other thing to check would be the heat riser on the exhaust manifold. With the motor warmed up check the radiator hoses and make sure they are not colapsing on you, if they are soft and overly pliable put new ones on. Run the car and turn on the heater to warm air you may have an air blockage, while doing this run with out the radiator cap. Good Luck