These following numbers are for Motorcraft/Autolite carbs. This number can be found on the side of the float bowl, right behind the accelerator pump rod, inside of a circle. The number on the right corresponds with the cfm rating on the left. Thanks to chas1234 for these numbers. The first numbers are the venturi size, the second is the corresponding cfm.
These numbers are for 2BBL carbs only.

Number = CFM
.98 = 190
1.01 = 240
1.02 = 245
1.08 = 287
1.14 = 300
1.21 = 351
1.23 = 356
1.33 = 424

These numbers are for 4BBL carbs, courtesy thrillseeker.
1.08= 480cfm
1.12= 600cfm
and a rare very rare
1.19= 670cfm.

For additional info on Motorcraft and Autolite carbs, check out this site:
http://home.earthlink.net/~bubbaf250...rb/carb01.html
He has a lot of good info on the history of the carbs, performance modifications, and carb operation theory.

 

Update: BubbaF250's Earthlink site has been dead for a while, I just found his new site:
Motorcraft 2150 2V Carburetor
Tons of tech info on Motorcraft/Autolite carbs.