If the steel crank assy was ext. balanced, Pull the pistons off the rods, find someone with a grams scale and weigh the flat top pistons and the dome pistons. If the flat top pistons are heavier than the dome pistons, you can remove weight by drilling/spot drilling below the pin bosses to make them the same weight as the domed one. You will then have the same balanced rotator. HOWEVER if the flat top pistons are lighter, you have no options except to re-balance the unit unless they are very close in weight.
There should be no difference in the stock external balancer and the fluid dampner since they are both counter weighted.
Some would say if it's a 6" balancer VS an 8" balancer, there would be a difference, maybe at 9,000 RPM's but not on the street.
Just don't forget to use the ext. balance flywheel.
Zip.