Cameron,
Go and talk to Norm at Aussie Desert Cooler and he'll set you straight. He reckons a well built copper core radiator will work just as well as an aluminium one. His work is exceptional and his prices are good too. He does tons of Hot Rod and custom car stuff and has a lot of knowledge regarding what does and doesn't work in a custom car setup. He's a real enthusiast and he seems to be more interested in building a radiator that will work well for your application than separating your cash from you.
He built the Aluminium radiatior for my car and I'm very happy. My reason for chosing aluminium was more driven by weight and cosmetics. Mine has a 2 row core but the tubes are about 1" wide.
Here's a pic:
Radiator
Cheers