Bigal21057
The intake port ID in a 235 head is 1.36 in. The ID of land machined in the head for the ring is 1.51. The Offenhauser manifold for the dual carb setup says the machined land in their manifold is 1.55 in. and the carb port dia. is 1.7 in. I could find no information about ID of the runners or the plenum of the manifold. It stands to reason that the runners are not as large as the plenum as the ring land is machined to fit 1.55 OD. I have been wondering myself if increasing the runner size or plenum size of a manifold slightly would affect the performance of carburation. I know the head intake is 1.36 in. and the carb flange ID is 1.56 in(for a Rochester), but in between them I don't know. Maybe some really smart carb guy can answer the question. My feeling is that if you keep the manifold carb port and plenum the same size, lets say 1.7in, as the Offy states, and the runner ID slightly larger than the ring OD. (1.55) you would probably be OK, but that is truly a guess.
