From the Offenhauser catalog: "The Dual Port and "C" Series accept the Carter or Holley STD bore 4 bbl carb.  Carb size recommended for DP is from 390 CFM to 500 CFM; for the "C" Series 500 CFM and larger.  Use Holley No. 8007 (390 CFM), Carter No. 9400, or Carter No. 9500 on Dual Port - Remove kick-down arm for linkage clearance.  Carbs clear "C" Series manifold without mod.  Offy universal linkage accessory kit is recommended in most installations.  These manifolds on a stock 240 or 300 C.I. engine can increase HP output by 50 HP!  Dyno tests on a Ford six with Dual Port manifold, headers, and cam produced as much as 115 HP over the stocker!"
Does not include hardware or gaskets.