In all likelihood your new pistons are not gonna be the same weight as te current ones, or not even close; so a rebalance is gonna be mandatory. Grab a balancer off any 360 of like style, and you are good to go. You will need a special puller to remove or replace it.
I have the puller the old one is already removed. The the rubber ring between the two pieces is rotten and the top piece is crooked. So if I can closely match the weight of the pistons it wont need rebalance?