14" fan + 360 = overheat

Aluminum is lighter. You can also make them thicker to hold more fluid and still not have the weight penelty of the copper.
I almost never ever had a day go above 100* here. (N.Y.) but it does happen once in a whihle every few years for a few days.
A hi-vol. water pump, good coolent in a good ratio, higher pressure cap and good air movement passed the rad are the main ingerediants (Hummm-sp!)
Anyway, after that, it's down to the tricks, water wetter, a plate on the back of the pump blades.
A thicker rad of 3 cores should do it well. 2 is not alot.