hello, I am building a 283 sbc and would like to know which carb cfm is better 500cfm or 600? been told that the 600 would be too big for that size of engine due to the heads. Motor will be bored, more for cleanning walls, rv cam, basically it. Just something to cruise around in and get decent gas mileage, Oh yea a 4bl carb and intake to add to list. Any advice. thanks