Correction -- You *could* use your 216 intake manifold .. but you shouldn't unless you want to choke it to death. The 261 needs the bigger carb/increased airflow, so use the 261 manifolds (or at least the ones from a 235) so you can use the bigger Rochester carb in place of the ole Carter W-1

-- a great carburetor (and one of the first inductees intot he Carburetor Hall of Fame, if I remember correctly -- Jon the Carb King can update us that that ), but too small for a 261... unless you use three of them

You don't have to relocate the water pump, or get a different front plate/motor mount if you find a '54 mold 261 (check out the conversation in
this discussion about 261'sAlso, read the Tech Tip (in the Tech Tip section) about rebuilding a 261.