unless your drive shaft is spinning above 5000 RPM, I would not worry about balance as much as you are. A standard drive shaft balance would be fine. I doubt if your running the shaft above 5000 RPM. with a 4.1 gear and 26" tires that would be close to 95mph. with a 3.38 gear and 26" tires that would be close to 114. Since these trucks are a brick - you will hit the aerodynamic limit before the drive shaft RPM limit unless the shaft is bent, out of phase, or improperly balanced.
If you have a 2-piece drive shaft, phasing is usually more of a concern than balance. As Steve mentioned, if your replacing a 2-piece with a long shaft, then you also need to worry about balance.
