All 216 and early 235 manifold flange bolt pattern is 2-11/16" on centers (S.A.E. #2), the late 235 and all 261 is 2-15/16" (S.A.E. #3).
The 235 and 261 carburetors use the same bolt pattern, but are not the same size:
235: 1-9/16" throttle disc, 1-11/32" venturi, approx. 200 CFM
261: 1-11/16" throttle disc, 1-15/32" venturi, approx. 240 CFM
The 235 can be used, but the results may disappoint you.
