Brady-
Many distributors for old trucks have replacement radiators. As Alan noted, they generally will have plenty of capacity. One thought is whether you have an automatic tranny with need for a cooler. That's one option you can look for in purchasing a replacement.
These replacements run ~$250-$300. While used radiators are out there for much less, they really vary in the ability to hold pressure (I own two ebay leakers!). You can have an old one re-cored if you want old metal showing in the engine bay.
