Boosted slant?

Many of the aluminum slant six manifolds had leakage issues, although if it doesn't leak under vacuum, it won't leak under boost.

Cast iron super six manifolds will not have leakage issues, but welding port injector bungs if you go EFI would be a challenge. I also would be concerned with a TBI about fuel distribution issues, although it may work. It may also be possible to prep a BBD (or two barrel Holley, probably more info about those) for blow through use.