It doesn't matter what crank you use, you need to have everything rebalanced anytime you switch cranks, rods or pistons. Even if they are the same size engine. Your engine should be balanced withing 3 grahams and those that don't know how much that is, a dollar bill is about graham.
It is correct that the 318 crank has less counter weight, but if you are running after market pistons, you will more than likely still have to remove some weight since most after market pistons are considerably lighter than stock, even stock replacement pistons are a lot lighter than stock.