Well, the Stave V dual quad manifold that I have has more of a "balance tube" connection between the front and rear plenums. I'd say that the connection is maybe an inch tall by two inches wide. When I looked at it, my interest was related to if the Idle Air Control valve in the rear throttle body (EFI) could get enough air to the front plenum while the engine was idling. The connector passageway should work fine for such low idle air requirements. But I wouldn't try to feed the front four cylinders at cruise RPM through such a small passageway. I suppose it would work ... poorly. And I think that there would be fuel distribution issues if you were using a carb. I'd take a better picture but all my junk is at MM getting screwed together. In the attached picture, if you look into the front plenum, right side in the picture, you can see a step up in the floor of the plenum. The top of the step up is the floor of the connector.