Radiators that for Desert heat

[FE_4_ME]

Ron Davis radiators is local to you. I had a double pass dual spahl(sp.) fan in my off road turbo car and it NEVER overheated. They are pricey, but worth it to me.
   

[billtroth]

I live in Illinois and certainly don't have the summer temperatures like you do in Phoenix but I have run the same Ron Davis radiator in my '64 Galaxie NSS car for almost 15 years without problems.

[BigNate]

I'm in the Phoenix area (Desert Hills / New River) and my '65 / 352 was my best friends daily driver for about 5 years when we were kids.   Pretty sure it has a <insert your local "cheap" parts store here> sourced radiator and neither he or I ever had cooling problems with the car.   This is with a simple arc of sheet metal over the ancient "flexi-fan" acting as a shroud.  He drove it daily in city traffic and we spent many 100+ degree nights idling in creeping traffic while cruising Central. 

I'm not suggesting that going cheap on a radiator - when I replace this one I'll probably do some sort of overkill aluminum unit - probably from Ron Davis or someone like him - but I'd be pretty surprised if a mild 390 would cause problems for an OEMish radiator if you get decent airflow through it. 

Just my 2 cents...