Cheeto,
The Offenhauser {#6006} 360* Dual-Plane/Dual Port Intake first hit the market in 1973.
* Style > 360* / Dual-Plane / Dual-Port / Plenum Divider
* Separate split/runners for the primaries and secondaries
* The design was, that the front {Primary} throttle bores supplied the lower portion of the runner ports.
* And, the back {Secondary} throttle bores supplied the upper portion of the runner ports.
* If anything, this Offenhauser Manifold liked 'rich' Air/Fuel mixtures, and with the throttle bores wide open.
* If the Carburetor was on the 'lean side', the performance was sluggish and with a low-end power loss.
* Peak Power was found at 6000 RPM's.