The venturi diameter has more effect on CFM than does the butterfly diameter. For example, Holleys with 1 11/16" butterflys range from 660 to 780 CFM. But the venturi on the 660 are 1 1/4" & 1 5/16", while the 780's venturi are around 1 3/8" & 1 7/16"
What you have there is a Holley double pumper that someone modified. But 4406 isn't a Holley p/n. The carb p/n was typically stamped on the choke air horn. Since that's been removed... ?