I also have a 454 in my truck I am having a bigger problem than you because my truck is GMC which has a different radiator than the Chevy. I have been researching this issue for a while and have been lead down the road several times by misleading information or information that gets contridicted by other vendors. I have found deminsional information on the US Radiator site for both the gmc and chevy as well as the small and large trucks.
radiators I would like to find someone who actually has already installed a radiator in the truck with a big block but I am having a hard time finding information. Hope this helps. If I learn any more I will post the info. Good luck.