How many CFM for my 340?

Hi, very nice car, it sits with a very beefy look. Color is a plus. I have ran allot of carb's on small blocks. The big spread bore AVS Carter is the nicest for a 340. But as you stated you have a square bore intake so that's okay, the Competition AFB is a great square bore carb. and you can purchase it with an electric choke. Mine was a polished one with 625 CFM and it had a very nice snappy throttle response. It also featured the option of stepping the idle circuit up or down depending on cam to stall ratio or in your case 4 speed ratio. And if you want more CFM a polished Edelbrock 750 CFM is available in the same design as the 625 Carter with the same idle circuit set up and electric choke. They are very nice carb's, very good for the street. Like one of the other poster's said the higher the CFM the higher RPM range. But I wouldn't go with less than 625 CFM on a 340.