IMHO a 2 bbl. is a win, but nothing larger.
Any 4 bbl. needs a very tall transition piece to re-direct the flow into the manifold, and the area of the throat has to be larger than the manifold's cross-section.
A Holley 390 4 bbl. with 1-7/16" throttle bores has to be necked down to a single 2-7/8" opening to avoid restriction - the manifold isn't big enough.
Even making the entry point an ellipse 2" wide by 3-1/2" long only moves the restriction away from the transition, since the manifold runner is way too small.
This is why adding a 2nd carburetor works: it only feeds the adjacent cylinder pairs, not the whole row of 6.
