My 451 Dart runs hotter than it should at highway speeds. But I can't decide if this is due to the old 26" copper/brass radiator having insufficient capacity, maybe in need of a rodding-out, or replacement with modern aluminum, or tif he Contour fans are acting like an obstruction when off.

Idling at a standstill, the temp will slowly climb to 198 at which point the fans kick on and fairly quickly drop it back to 192, then they turn off. Repeat indefinitely.
When driving at 30 (or 60) mph, it wants to run 196 or so.

If I manually turn on the fans while at speed, the temp will drop some, but never all the way down to the 180 thermostat.
Think I just answered my own question - most likely the radiator.

Any recommendations for an aluminum one that won't break the bank? It has to be fairly thin to clear the Contour fan assembly to water pump pulley, and they are a perfect fit across a 26".

I'm not sure exactly what I put in there for pulley ratio or water pump (a/c or non-a/c) - could it make that much difference at 2000-3000 rpm on the highway?