Most Motorcraft 2 barrel will have the venturi size stamped on the side of the carburetor. In this example it is 1.21, which is the size as illustrated. The smaller the venturi size, the smaller the engine. Don’t put a 1.33 on a 289, or 302 engine and expect it to operate correctly.
0.98 = 190 CFM
1.01 = 240 CFM
1.02 = 245 CFM
1.08 = 287 CFM
1.14 = 300 CFM
1.21 = 351 CFM
1.23 = 356 CFM
1.33 = 424 CFM