CNC-Dude, Before there was a choice of intakes we would make 2" and 4" spacers to go between manifold and head. The 4" showed the most benefit with the Offy 3x1 setup.

I would like to see someone make a 4BBL manifold with the center runner coming into the plenum from the bottom as far as possible to the outer side. The end runners entering from the sides. This would require a raised plenum. That would mean more cores I know. This would more than likely be a race only part.
Just my thoughts.