One thing, when NEW, Chryslers with factory a/c usually did NOT have any cooling issues that we could see in Texas. GMs did, but not Chryslers. FEW people even kneew about electric cooling fans.
Get the block cleaned out with new core plugs, to get the accumulated gunk out of the back of the block, which is the lowest point in the cooling system, so that's where it usually accumulates. Using a caustic flush component can harm the heater core and such, too, so best not to use it.
As to the radiator? Just the stock factory a/c radiator should be quite fine. Back then, Chrysler had a proving grounds in Arizona, so they tested for "hot weather", no doubt. Thee radiators worked plenty fine back then, so why would they not do similar now? IF you get the core replaced, aim for one that is "high efficiency" as to tube width and such. Forget the high-priced and trendy aluminum "stuff" on the market now!
DO aim for the Robert Shaw style thermostat like Chrysler used OEM back then. 180*F is all that's needed. NOT the style that most everybody sells to replace them. Better temperature control and flow.
Similarly, get a water pump that has the correct number of vanes on it for the a/c cars. NO variations! The pump drive ratio changes with the a/c cars to spin the pump faster than the non=a/c cars.
FORGET any of the "high flow" water pumps. They can, in their best intentions, move water through the engine TOO FAST, which results in less heat removal per pass. I neded a water pump for one of my cars, so I went to the local auto supply which had life-time warranties on them. In looking at the casting, it looked smoother than OEM and cleaner, so I was happy to get it. Only thing WAS that the temp gauge ran one needle-width higher with this visually superior pump!! When that one failed, I got a "factory casting" pump and the temp gauge needle went back to what it had been. AND that auto supply chain had left the region when I needed that new pump!
IF you want to spend the money, you can try the Evans Coolant which Jay Leno uses. Might be better with benefits of longer life, but $$$$ to make the change-over.
ONE other thing to consider is that "over-heating" does not start at 190*F, but at 260*F (which is the boiling point of 50-50 coolant with a 15psi radiator cap. I don't like the needle to get past the 1/2 way point, consistently, but until the heat gets to the higher levels, it's all good AND should come back down later on.
My main point is . . . the cars did well when they were new, so if they are back to OEM-production "like new" cooling system condition, there should be NO need for any of the stuff that people tend to key on in modern times! Like aluminum radiators, for example. Although a "heavy-duty" Hayden fan clutch can be an asset.
I know what I lived through with our '66 Newport 383 2bbl factory a/c car, back then. A/C blew cold and the "HOT" light never flickered. Just a trait of those cars, back then. Even when the temps were at or over 100*F in the July and August Texas summers. Always used Dana/Perfect Circle OEM-style fan clutches, too.
When stopped, keep a distance between your Imperial and the car in front, so better airflow can get to the radiator/condenser. Hopefully with it "nosed into the wind". Just common sense things, to me, but I mention them for good measure.
Just my experiences and observations,
CBODY67
