I put a 500 Cadillac in a 51 GMC AD that now has over a quarter million miles on it( 2nd engine). It has a/c and is in the Texas heat without ever going over the thermostat setting. The radiator is out of a 46 Ford truck with a flathead 6 in it. It did require four copper tubes run from front to back of the top tank and soldered in place so it doesn't flex the tank and crack the tank to core joint. You can see it at: http://s32.wwwphotobucket.com/albums/d41/coilover
Scroll to the bottom of the first page and click on page 3 then scroll down it to the blue 51 labeled 51GMC/500.

Evan