Offenhauser was the dominant manifold company in the 50s and 60s. Because of that I think they tried to be "creative." If that Dual Port design would have been legit I have to believe Edelbrock, Weiand and Holley would have made a knock off of it. To the contrary- Offenhausers best manifold- the Port O Sonic looks like a Holley Strip Dominator, Weaind Team G and Edelbrock Victor. Im thinking Offenhausers outdated single plane manifolds were poor compared to the other single planes with swept runner design so Offy decided to make the sonic. BTW- Offenhauser NEVER made a true dual plane manifold. All there units were a big open single plenum/cavern.