The "old" style heads don't flow as well as the VVTi heads, however if you're force feeding them, it's not such a big deal.
Are you looking at centrifugals, Roots, or screw compressors? Roots & screws need a dedicated manifold, or a DIY one, while centrifugals only need a fish bracket and some custom piping.
You may have hood clearance issues with the Roots and screws.......