Are you refering to the intake manifold or exhaust manifolds? For an intake, there is no distinguishing a standard from an HO - they both have the same part number. I think there is a different manifold for the 326 (Carter Carb) in 1967, but that's also the same P/N as any other non-rochester car.
For the exhaust manifolds, check out several other threads on long branch exhaust manifolds. These are the "HO" exhaust manifolds for a firebird (Except 326 and 350 HO - I think.)
