322 Buick nailhead I'll bet. They were offered in the big trucks from '57-'59.
Being a Buick fan, I'd go with a nailhead. It doesn't have to be a 322. The newer nailheads are easier to find and parts are more available.
Carl, you nailed it. Chevy with the 283 need to fill the gap until the 348 came out, so 322 Buick filled the gap.
