The Zx550 pistons have a higher crown with deeper valve pockets, but the overall compression ratio is the same as the earlier Gpz's so the overall combustion chamber volume has to be the same. But I'm not sure if it's only the pistons that are different, or if the head has a different shape chamber to make up or take up volume. That is, I'm unaware of any volumetric differences in the head in regards to compression ratio.
According to Kawasaki's Parts Diagrams, the H and A Model Heads are listed with different part numbers. In my years looking up parts for the GPz550, the part number can change from year to year if there is something as a different paint used for the same part. Not owning an H Model Head, I only know the A Models. Head Gasket shows to be different, and even the intake holders are not the same. Intake holder o-rings are even shown to be removed from the A Model, but they still have the groove for them, so I'd still use them.
Unless you have them side-by-side, I wouldn't be able to tell the difference.
Thanks for the answer and the link to the information about the cam switch. My thought was to switch to zx camshafts as you mentioned. I'll read the informative link you provided and then decide if I'm going to change cams.
Again thanks for your reply.