For 2 barrel Motorcraft/Autolite carbys the usual venturi size for a c-code engine is 1.14 inches. This is marked on the side of the float bowl inside a circle.
I have a 1.21 inch venturi Autolite carby that I will fit and this will increase flow from 300 cfm to 351 cfm.
Some of these larger versions were fitted to early Fairlanes, Falcons, Broncos etc.
See below for 2 barrel venturi sizes in inches and relative flow in cfm.
0.98"=190 cfm
1.01=240
1.02=245
1.08=287
1.14=300
1.21=351
1.23=356
1.33=424