Carb cfm with ported heads?

My street 4" engines run wet flowed vacuum secondary 870s. These cars also run 3.23 gears and convertors that stall under 2500rpm. They manage high teens in fuel economy in heavier cars (E bodies). The right carb is probably a bit bigger than you think. BUt you can't really go wrong by going bigger. Unless you can't tune. Smaller carbs are easier to get well tuned.