The 2100 2V carburetor is specific to each engine and transmission combination. 2100 carburetors were made for both small and big block engines. Big block carburetors cannot be used on small block engines because the butterfly valves hit the manifold openings and stop the throttle from opening all the way. Manufacturing tags were not used until 1965 but, the throttle bore size can be found cast into the body of the carb on the drivers side towards the front.
The 280 and 289 engine 2100 carbs had a 1.01 or 1.02 inch venturi opening which translates to 245 and 240 cfm respectively. Venturi size was determined based on the engine and transmissions. Cars bound for California received smaller jets as did cars bound for higher elevations.
The 4100 series carburetors used on 1964 260 ci four barrel applications had a 1.08 inch 480 cfm body. The 1965 289 4bbl carburetor had a 1.08 inch venturi as well. However the High Performance engine carburetor had a 1.12 inch venturi to get 600 cfm.