Dave,

My 261 and 235 carbs are interchangeable (at least as far as bolt-on goes - 1.5" flange). However, I understand the 261 delivers more gas than the 235 carb (different venturi throat size).

The 216 has a different bolt-on flange size. I am not sure about the pre-1954 235 carburetor bolt-on flange size.

As Brian stated, you most likely have a 216 carb (37-53) and '54 or later 235 engine. The carb and intake manifold do match (53 and earlier to 54 and later).

Tim