A freind of mine has a 1961 Chevy truck with a 496 cubic inch, 850 hp engine. He called Be Cool (
www.becool.com) and told them the year of the truck and what engine/transmission combo he was using, and they custom built an aluminum radiator that simply bolted in with absolutely no modifications. This truck was his daily driver for a while, and never overheated in the 100+ West Texas heat. I don't remember the price, but it was very reasonable.
Also, Be Cool suggested using a two-core radiator with 1" coils instead of a four-core with smaller coils. They claim that the air is too hot by the time it passes through the other coils to cool the last coil in a four core radiator.
Hope that helps.
Phil