As far as I go everytime I've seen caps moving there has been some det. now undoubtably if you run aluminum rods it will help because of the shock absorb effect the rods have on any engine but you're going to need to be careful because in the tune you acn also beat the rods out of round due to det. on high boost and power applications over balancing the cranks also helps cap walk thats when you increase the balance factor and counterweight the crank heavier then the actual assembly. We overbalance all of our alcohol funny car and top alcohol blown drag race stuff. Run these things by your engine builder and I'm sure he can guide you in hte right direction.SIncerely Laz Mesa
P.S. The overbalance is extremely important in blown alcy engines.