Ever been in traffic on a hot day in your classic and watched the gauge gradually move over 220 knowing it’s not going to stop unless you can get moving and get some air flowing?
Those old copper and brass radiators just weren’t made to handle it. The newer aluminum radiators do a much better job by using larger tubes.
Manufacturers such as Griffin make custom fit radiators for most vintage cars and trucks. If they don’t offer one for yours, a universal can be adapted or they will custom build one for you. Replacing the radiator is probably the most effective way for us to keep a car/truck cool.