400 cfm AFB?

You might do some research on the AFB's that came on the '64 - '65 Buick 300 and '66 - '67 Buick 340 engines (yes, Buick had a 340 before Mopar did). I have had these cars in the past and those carbs had some pretty small butterflies and venturies. I would bet they weren't any bigger than 500cfm but they could be smaller.

Chuck