So the problems almost gone now, turns out the spigot on diff was .3mm undersize, and bolt holes being super neat, when loosened off I wiggle plates and no play... The manager/engineer came and inspected the setup, and detected this, took it back, made new spigot perfect size, re-balance again and sent back and I fitted it, and now it runs great to 110 km/h but 110-120 it has the same vibration however nowhere near as severe as before, its just annoying now. Everything setup and balanced perfect we are at a loss as to what the issue now is. The only thing suggested was the unis, as they are a solid centre type, have fibre thrust washers on ends to stop play, and inturn offer resistance, the possibility is they are just tight enough to begin vibrations at that speed. IF this is the case, it'll pan out in the next few hundred kms.. I hope so. Input?