CID x RPM x VE gets you the same basic number as using HP for carb sizing.
323 cubes at 6500 rpm only needs about 650 cfm. So something was wrong with the 750 carb. A properly built 650 carb on that engine would make more torque and go down the track faster than the 850 that is on there now.
I never agreed with that formula... a 1050 dom would be way to big on my 405.. yet every carb that was bigger went quicker/faster