i believe that the 9" diff was a ford design, but can they claim the watts linkage as well??? as far as i know they have to use the manufacturers blocks i.e. GM and Ford but i believe the heads are open to the teams. i also beleive that all the teams run a modified version of the watts linkage where the central mounting point is attached to the car and is adjustable(reffered to asthe rear roll center adjustment)where as, on the original watts linkage the central mount was attached to the back of the diff casing. i also remember HSV tweaking the rear suspension by the inclusion of an extra link somewhere but what ever HSV did, didn't Holden adopted this "tweak" as standard in the following model, s2 VX i beleive. aren't the 9" diff mandatory as are the available ratios and the 6 speed hollinger and ratios as well to create "parity" between the manufacturers:ranting: