Balance has nothing to do with what the total weight is on the back or front of the crank. It is where the weight is distributed in relation to counterweights, etc. If a motor is internally balanced, swap away! No problem, if the motor is externally balanced, problem. The problem is the manufacturers tolerances. We had a customer with a 454 in a dragster and due to his own stubbornness he ruined 7 flexplates, since we built the motor we rebalanced every one of them to the original offset weight. They were all SFI approved and of 3 different manufacturers. The weights were off by as much as 11 degrees and 24 grams at 6". It would have shaken with all but one of them. The manufacturers half-ass balance to somewhere near zero, and then just weld on the weight with a fixture for the externally balanced stuff, they don't check the offset weight after they are done. The same holds true for Chrysler torque convertors which have the offset weight on them. Any competant shop can balance the flywheel to the flexplate or the other way. All it takes is a computerized balancer. About 10% of the balancers in the area can do it. The others have old-type units. We charge about $20-25, depending on how long it takes. TIMINATOR