[BruceWilkie]

Slick1 the manifold has to 1) compliment the runner in the head to get the most out of it. If the head port flows a given number and the manifold flows the same number it does NOT mean they will work in concert with each other and still flow the same number into the cylinder. Properly executed their is potential to gain overall flow. Think complimenting angles/shapes as the flow transitions from manifold to head. 2) equal air flow in opposite direction does not address what happens when fuel is added to the air. Fuel and air though both "fluids" have different dynamics due to weight. Even with dry flow there are aerodynamic considerations. Primarily venturi like effects. An exaggerated example would be flowing a carb in reverse, but the principle is what I'm pointing out. Bryce Mulveys method makes sense on an exhaust manifold outlet providing he goes in the direction of flow of course.
Personally I hope a lot of the Chevy boys do it his way on their intakes.