Almost right John,
The Offy 4 barrel adapter allows any of the Edelbrock/Carter squarebore carbs to be mounted. I have a spacer on mine so that the throttle linkage will clear the intake runner. Mine has an Edelbrock 500 cfm 4 barrel. Works great.
To answer the original post, from what I've read (and it logically makes sense), the Clifford does flow more than the Offy - just by having larger runners. I believe the Clifford also flows better due to the aforementioned angle differences.
I believe the ideal street rod intake for the later 6s (230-292s) would have the Clifford design and shape with Offy sized runners. Water heat hookups (like the newer Clifford street manifolds currently have would also have to be factory cast in for good streetability.
-magic mike-
