[Boog]

If you want to drop a stock 350 or 455 olds in the truck you won't be out a lot of extra money on it. And if I'm not mistaken the 455 drops in using bb chevy mounts. It won't be as cheap as a small block chevy for a small block chevy swap since stuff like exhaust and a different radiator may be necessary.
As said it's the performance parts that'll really cost you.
I dropped a 350 olds in my 56 ford pkup back in the early 70's. I loved it. With a 3.73 gear it was fun. A 455 would be just that much more fun. And not to mention olds engines aren't that much in demand these days one should be reasonable to buy.