600 CFM, all I need. Check my math!

Your math is correct on approximately how many cfm's your engine needs. But what that formula don't tell you is which carb you need. No matter what carb you run is gonna with in reason will pull 561 cfm's thru.

Just cause you run a smaller or larger carb your engine isn't gonna all of a sudden use more or less fuel and air.

What you got to decide is how much vacuum you want to pull at full throttle (restriction). So 1.5" vacuum should be close the fourmlas out but be on the restrictive side probably want to be around 0.8-1" probably the carb you have now.