Never had the problem at idle, but at cruising speed is another story. If your at an idle, and it gets hot, your cooling system isn't flowing enough air, and your water pump might not be helping as much as it should at low speeds.
Ever go to the car shows and see/hear a performance engine and look under the hood only to see that they upgraded the engine with headers, a new cam, heads, and intake, but stuck it back into a stock engine bay with the stock radiator, fans, and damper. At certain levels, it requires other things to be upgraded as well. The stock water pump with throw fit tolerances thats now 35+ years old isn't going to flow well enough to really keep up, nor was the stock rad that they had re-cored able to keep up. You need to address the areas that support the upgrades. Even if you want it to look stock, a brand new pump and radiator will out perform the old units by a bunch just by the newer manufacturing tolerances.
Would you run a points ignition on your $5k rebuilt 440, or would at least bring it up it to the basic chrysler orange box kit? When you get to the next level, you need to upgrade again, or performance issues show their ugly head in weird ways. As the saying goes, all the parts gotta match.
