I'm running 2 AVS2 800 cfms on my 440. If you are buying new carbs, buy the AVS2 series. They have annual boosters on the primary side. Very nice for throttle response.
For a dual quad 318, the 500’s would work just fine though I’d run a pair of 600’s. Your set up is not very radical. You could do 500’s if you desired. The carb choice would be the AVS 2. They have an advantage over the earlier AFB style with the primary annular boosters which are really nice on throttle response & fuel distribution. The adjustable secondary air door is very nice as well.