If you are going back to STOCK rods and 9.5:1 pistons, then try to find a piston that are as close as possible to the weight of the STOCK pistons. You may be able to bring them closer to stock weight if they are a little bit heavy, and if so, balancing won't be necessary. If they are heavier then the stockers by more then a few grams, then yes, balance it.

This assumes that the crank and rods you use have not been molested. I have also heard that the stock balance was poor, but, I've also read that stock balance was pretty close. I think that's a toss up.