Cooling Issue - 1964 Dart GT - 273 with automatic and A/C

Syleng1 said
As a guy who has a highly modified 273 commando engine in my 66 barracuda with auto and ac. Mine has a factor radiator and fan shroud and clutch style fan. No issues getting hot. I tried the aluminum radiator route and honestly it had a tough time like yours does. I’m not saying the aluminum is the issue.
The temp fluctuates a lot with aluminum.
Also, with gauges that are 60years old verify they are operating properly. May be a aftermarket gauge installed will show your factory gauge is out of calibration. As for the engine, normal stuff to check is:
Water pump (cast iron unit)
Thermostat
Hoses
Blockage in the coolant system - drain and flush the block.
Ignition timing
Running too lean.
Slipping converter / transmission.
Just a few.

Syleng1View attachment 1716291558

Very nice engine bay you have there! Thanks for your input. The gauge operation tends to correctly follow conditions, using an IR thermometer. But validation with an aftermarket gauge may be a good idea. Can you recommend one? Also, where did you find your stock radiator, or is it original? Are the mounting points the same dimension described above? About 21.25" on center? Water pump is building pressure and you can see flow in the radiator, so I made the assumption that that wasn't an issue. I'll revisit timing and carb lean/rich settings. Can you elaborate on the slipping converter/trans?