My 66 Lemans originally had AC, I ripped that out.....But AC cars had extra cooling features (that are even better without the condenser dumping all that heat in the engine compartment)
First they had 4 core radiators, and seven bladed fans I kept both those features. But I had US Radiator build me a coppper 4 core radiator with extra large down tubes. That thing looks like original, but cools way better than even the original 4 core. ( Now it does not have the stamped “Harrison” on the top. Like the original if you need that for originality, I don’t care about that.
I use a thermostatic centrifigal clutch, heavy duty. The RPM clutch has a flat plate on the front, the thermostatic has a little circular spring, make sure that you use the one with the spring, the cooling difference is very noticeable. Also make sure your fan clutch is fresh, they lose the silicone fluid slowly, and add temperature gradually, you will notice it mostly at idle. Feel the fan blades......car off please! And see if they feel greasy or oily, it is usually the leaking silicone. Change the clutch.
I use a Flow Cooler water pump with very tight tolerance on the inside plates, an 11 Bolt Water pump as well. Make sure the fan is half way into the shroud, if not you will lose a lot of cooling, and your shroud and rubber surrounds seal it as it should, it does not have to be air tight, just properly blocked.
Make sure you timing is right, retarded idle timing will make the exhaust run hot and therefore the engine. You need about 20 to 24 generally at idle with 10 from vac advance.
Make sure your rubber shrouds are in place in the fender wells, Ames sells them, I think they are $11 each, they will make you run hot if not there because it effects proper air flow through the engine compartment, the radiator needs that suck thru as designed by the engineers..
Some guys rip those out or they deteriorate, put them back you need them.
Of course good hoses clear passages and a new fresh Radiator cap so your pressure is at 16 lbs.....it all matters and it all works together