This carburetor is one of the hardest carburetors to identify when it comes to purchasing rebuild kits. Fortunately there are ways to find the original carburetor number, or worst case and with a little work, you can at least get the correct carburetor kit.
Identification. Rochester used a tag attached to one of the float bowl screws.
Some of the B type carburetors also had the number stamped on the face of the base (flange).
Some Rochester B carburetor were produced without tags. On these carburetors the last 4 digits were stamped on the bottom of the throttle body. The carburetor number was also stamped on part of the air horn gasket, but the chances of the original gasket being found is pretty low. Add 700 to the 4 digits.
When all else fails you can figure out which carburetor kit to buy by inspecting the accelerator pump. The older Rochester B carburetor used a flat stem pump and and is found here. The later Rochester B carburetor used a round stem pump and is found here.