Gibson makes some tubular exhaust manifolds for '88-'98 fullsize halfton GM pickups, I'll bet these would match right up to either an '87-'93 5.0 H-pipe, or a 351w-swap H-pipe. If you're interested, search
www.summitracing.com for SUM-G9014-9. I don't know if these would clear your steering.
For long tubes, I guess I would start by trying some for a '67-'69 Camaro.