GPz750 pistons no good for a ZXR mate - they are 2-valve pistons. They also use a 15mm pin, which may or may not be the same as a ZXR750 ? Stock GPz750 piston diameter is 66mm, same as the z900 models.
Good luck with the search, anyone building a kwakka motor to beat those spewzukis deserves as much help as they can get
