New pistons / re-balance?

You have to remember the weights we are talking about in terms of imbalance are in grams. If you replaced stock pistons the new ones will be lighter. The factory cast pistons have expansion limiters (steel bars) in them and they are heavy. The performance replacements are lighter by a bit usually. You could run with the crank a little heavy. It's called "overbalanced" and it is used to help some engines with shift recovery and throttle response in circle track builds. But really the only way I'd run without balancing is without replacing pistons. Factory balance jobs can be as far as 20g out. So if you can get weights for both and they are less than say, 10-15 grams, you might get away with it. I wouldnt advise it. But it might work.