1976 Dart Overheating and other issues

My first suggestion would be to flush the cooling system with what you can find at your local parts store, then get he radiator cleaned properly. My final suggestion would be to go to "mymopar" & download a factory service manual (FSM). Read up on the cooling system & tuneup, including timing. I think if you follow these suggestions, you maybe able to solve a lot of your problems. Along the same vein, get an infrared temperature gun (Harbor Freight) & check the temp at the radiator & stat housing to see if your gauge is close to accurate.