Welcome to the board! There is a TON of useful information here! Fire up that search engine and find an answer to just about anything!
I don't believe that Carter made a YF for the Chevrolet 261 engine. If you don't want to use the original Rochestor, then I suggest a Zenith series 228. This is the carburetor that was used on the GMC 270 engine. It's CFM rating makes it a better choice for the 261. You certainly can use a YF carb for the 235 on your 261, but your engine will not live up to it's full potential. I used a YF2100 on my 261 for a while. It was thoroughly adequate.
I'm now using the Zenith 228 carburetor on my '54 261, and have no complaints. It was a direct bolt-in with no modifications needed to the linkages.
However, it can be a somewhat hard carb to find. I was fortunate and found mine on ebay for dirt cheap. I had a local carb guy professionally rebuild it.
Happy 'bolting to you!
Steve
