If no one chimes in here, I'd suggest removing a a shaft, it's axle nut and companion flange and carefully count the splines. One question pops to mind though, and that is "why were the threads trashed?" This thread problem is typical with the "peened" nuts that were flattened against the axle stub "flats" to prevent the nut from backing off, but on ALL the ZX turbo cv jointed shafts I've ever seen, the nuts were changed to the more traditional locking nut that does not trash the threads when this nut is removed (perhaps an impact wrench's high speed removal of the nut caused this). There is only a 2 spline (?) difference between the 280z and the 280zx turbo splines (turbo being smaller or less count). I do not know if this difference was carried through onto the ZX line or not (turbo vs non-turbo). If your non-turbo axle nuts are peened onto the axle "flats", then I'd be inclined to believe this difference may exist.