Assume the heads are cast iron. What's a common temp range they run in cold or hot weather?

Cast iron heads??

If you are running cast iron clunker (big bore 100+mm cast iron cylinders) you can expect CHT at minimum of 350F if you are lucky..

Where is your CHT snsor?

CHT isn't effected much at all by ambient temp differences, mine run the same winter or summer in all my cars.

Yep 103mm cast Iron Clunkers I don't have a gauge, just using the stock cht and am looking into the hooking the gauge that works off the #3 plug. We hit it with an infrared gun on the #3 cylinder and it was reading 280 after a nice long drive. Oil temp was running 217, (using brad penn 20-50) Don't know what the oil pressure was because I haven't put that gauge in yet either. Working on those 2 gauges.

The infrared is worthless. CHT can drop 100 degrees by the time you pull off the road and open the decklid to shoot that worthless meter at the engine. These gauges read surface temperature and too often thats the temperature of the fins, not core temp- so its worthless..

Install that CHT, then we'll talk.. I wouldn't be driving that car with those cylinders without that CHT installed!!