I just balanced the blades for mass and spanwise CG. The head itself shouldn't be bad right out of the box, but if you want to check you can use the heli as a fixture- without the gear on the mainshaft, temporarily hold the airframe in a vise so that the mainshaft is held out horizontally in the main bearings and can spin freely.

Do remember that getting this absolutely right can be difficult, so if it seems like the balance is off, you may not be getting accurate results. Until you get to fly it, I'd not go beyond balancing the blades.