1976 Dart Overheating and other issues

Lots of good advice here. I too see that thermostat housing and would think that the radiator is plugged. Radiator shops are few around here and expensive. Probably cheaper to just buy a new one (bought larger 22" Air conditioning one for mine for 180). That said, I wound not replace it or have it rodded until I was sure all that crud was out of the block. Might be best to pull the water pump to do part of this. I've read of people using vinegar or dishwasher soap to clean cooling system. Might look into that. I'd also rig up a strainer (try McMasterCarr)on the the input hose until it is clean. Dont want to plug a rodded or new radiator.

Another non cooling system issue not mentioned yet could be the heat riser.