1976 Dart Overheating and other issues

Mako21 said

Also, when flushing the radiator, I see three outlets at the bottom of the radiator. A plug at the drivers side, then moving to the passenger side a pipe that I assume runs to the heater core? and then next to it the rubber hose running to the water pump. Do I pull all 3 to flush the radiator?

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Really could use more information here. A few pictures of the engine and radiator area would help out a LOT! It would be nice to see what fan is there and if it has a shroud or not. 20 miles at what speed? Was the A/C on?
Buying an old car is like a box of candy, you dont know what you have until you bite into it. Assume nothing as far as maintenance issues go. Until you verify everything, you dont know where the problems are. Do not fix things that aren't broke or do too many things at once.

Look on the firewall above the engine on the passenger side and you should see 2 rubber hoses approximately 1-1/8" O.D. Those are the heater hoses leading to the front of the engine. They do NOT go to the radiator.

There is a petcock on the bottom of the radiator that drains the radiator. If you have an automatic transmission, there will be 2 hard lines that lead in and out of the transmission to the lower radiator. Do not mess with those as the radiator also is used to cool the transmission fluid. If you drain some of the coolant, look at the color. It most likely should be green if the right coolant was used. If it looks brown, you should change it. A 50/50 mix of coolant and water raises the boiling point of the fluid. Look for blockage at the front of the radiator. The fins should be clear without blockage. You can squirt a hose from the engine side towards the bumper to dislodge the junk. Hell, If it was me I'd drain it and remove it to get a good look at it.
Factory gauges are kind of approximate indicators. Running at 220 is nothing to get upset about if the cooling system had been verified to be in good shape.