>Cooling in these Mustang has always been a challenge with high horsepower engines.
True that. You can fit a 19" tall aftermarket unit in a 69/70 but the width is a challenge. The 31" wide unit I have drops in my Falcon easy and clears the side rails. Just trimmed the core support a bit to match the core width. Not so much room in a Mustang. The 70 had a 26" wide unit, IIRC. That and a couple of cheap eBay 12" fans on a formed shroud with a Flowkooler pump and the bitty Moroso drive motor was good enough at the drag strip. The car would stage at 180 and come back from an 1/8 mile pass at 200~210 then cool down in just a couple of minutes.
As for the core, there are no 26" cores in 67-70 FE or AC cars. The original 67 core is actually 23" and the 68-on is a 24" core. No one is reproducing the 67 core so it forces a change to the 68 radiator and a change in bottom mounts. I agree with you, managing heat in many hot climates is difficult.
Not everyone is drag racing or is going to cut up a car for cooling. Especially original FE cars or Shelbys. The cars didn't overheat new. So there has to be a formula here to resolve the issue.