[smittyseng]

I have a set of 1974 SD 455 roundports laying around and am making a game plan for upgrading/rebuilding my 421 in my 1966 Bonneville this winter. I have a good 455 crank, sd rods, sd heads and sd exhaust manifolds, SD 455 block has freeze cracks. Considering boring the 421 to 455 bore, dropping in the 455 crank, rods and heads but I am pretty sure the sd 455 exhaust dumps on manifolds will be in wrong place, aside form headers is there a round port exhaust manifold that will work? I might just broom all the 455 stuff and use the money to have the stock heads cnc'd at sd perf and rebuild stock short block, buy long branch exhaust manifolds, or do that but put 455 crank/rods in, then machine valve reliefs in the pistons to match the original heads, just sorting out my options, thanks for input, Smitty