My lightened pistons are around the weight that yours are, although most aftermarket pistons weight about 420+, the low comp GPM +060 pistons I had weighed 428g each from memory, my Ed V pistons (lightened) weigh similar to yours. I've never balanced a crank myself so can't help on that bit although I've found 62% gives a nice smooth motor on a dry frame bike. How are you going to account for rocking couple?