I have 2 Rochester Bs made for a 261 and both have warping issues that cause internal and external fuel leaks. Also, there is some wear in the accelerator piston bore. I am one of those who is not fond of the B, so I decided to use something else. Heads-up info:
In 1960, the design of the Rochester B changed to a different mechanical connection for the air cleaner. The Carter YF for Chevrolet changed as well. This is just one of the "gotchas" that you can run into when looking for a different carburetor for a 261. You also can have throttle linkage issues such as type of bell cam, on the engine. Then there is a difference with the Carter YF models (Chevrolet, GMC, Ford, Jeep etc.) where throttle arm up = throttle valve open versus throttle arm up = throttle valve closed. Then another carburetor issue of ported versus non-ported vacuum connections for the distributor timing advance. Then some of us prefer a manual choke carburetor for our "Stovebolt" engines. It's not fun to spend $$$ on a rebuilt carburetor only to run into the adaption problems. Homework is required. If you are rebuilding your 261 then you need a known good working carburetor before attempting the engine break-in run.
I have a Carter YF 2100 on my 261 in my 55 1st. Cold cranking is excellent even after a month of sitting. The only issue is that it was designed for a 235 engine, and you lose a little bit of power going uphill full throttle.
