Turbo slant six post

Doesn't seem like 250 cfm would be enough????
I too have a weber 32/36....read they are 300-350 cfm.
Also have a Rochester "VariJetII" off a lates 70s chev six. It is suppose to be in the 350 range. (basically half of a QuadraJet)
Can you tell what cfm a carb is by measuring the butterflys?