I used a "universal GM" radiator by a company called UNIVERSAL PARTS INC. out of Wisconsin. Quality is great, service is great, and they can do custom modications for cheap. This the one I bought. $399 - comes with shroud and fans. I had them weld aluminum tabs on each side for something like $30!
check out there selection.
http://cgi.ebay.com/ebaymotors/19X31...0134QQtcZphoto