I did a similar swap, I put a 455 with 16 heads into an 85' Chevy 3/4 Ton 4X4. The truck has headers and 3" pipes, and a TH400. It needs cab work and a timing recurve kit but it ran a 16.1 at 85 mph, at 5,000 ft elevation. I didn't think this was too bad for a big, non areodynamic, brick.
The headers are a lot of work and if you are considering a swap the only problem is clearence over the front diff. I ended up customising a pair.
