After A/C Add On Engine Overheats Really Bad

Toss your fan and thermostat in the garbage.

Get a real clutch fan that moves some air. Get a 180 stat. Get a shroud. Make sure your hood to core-support seal is there.

Get the car properly tuned.

See where you are after that.

The stock cooling system on these cars would cool just fine in Arizona heat back in the 60.
High compression, AC and all....
It's when people think they are smarter than Mopar engineers that problems happen.