What size carb?

I have a 72 318, stock bore, edelbrock performer cam, edelbrock performer intake manifold, 302 heads with mild porting, stock exhaust manifolds, 3:55 sure grip. Right now I have a Holley 650 carb on it. Is this too much carb for the motor. If it is what size carb should I look into. I was thinking maybe an Edelbrock 600 or trying the Summit 600 that just came out.

I will be building a mildly worked up 340 in the future. If I take the Holley 650 off the 318 do you think I would be able to use it on a 340 with some mild work done to it, or would it be too small.