A bunch of us can reface your disc. You could make a static balancer out of bearings and blocks, which will get you very close. There qreat ways to preserve the dynamic balance, but that will depend on how material is taken off. (large decision tree type stuff).
The best thing is to mount it on the lathe true to the bore and measure with a plunge or test indicator how out of true it is. The short story is if you are taking out a skim at one position (say 3 o'clock), you take off the BACK a similar amount of metal on the opposing side (for instance 9 o'clock).
There are shops that will dynamically balance it for you, but that will cost you more than the plate is worth.