The central hole on early LI stators is smaller than on later spec stators as the centre boss on the early flywheels (brass 6 pole) was smaller, however, later Ducati centre bosses where bigger. If you try to use the later flywheels (including GP Ducati flywheels) on early stators then they normally rub and burn out within minutes of starting them

This modification is talked about in greater detail in the Official Home Workshop Manual (a must for all SIII/GP owners).
Adam