While admittedly I'm not in the same climate as you my experience is that mopar stuff is significantly cooler running than gm or Ford stuff of the era.
So much so that in the 80's it was commonplace to put a 195 Stat and a restriction in the bypass on small block Chrysler in order to make any hear in the winter.
Every time I've seen a stock or mild small block Chrysler overheat it was a stuck thermostat or to small/plugged radiator.
Some of the early a bodies had a tiny rad and can't take much contamination before they affect cooling ability.
I'm also a big believer in clutch fans and shrouds. The biggest clutch fan you can fit,the biggest rad you can fit and a shroud that puts the fan blades roughly half in/out of the shroud is always a recipe for success.