Any of the ZX-6 series from the late eighties through to the end of their production, late '90's, will fit. They're the same. It requires filing the radius off of the 600 riser where it mates with the top tree. The 600 is radiused where the 500 is straight on the plane with the two bolt holes, setting into the recess in the top tree. Bolt-on in all other respects. It will also clear the tank and gauges but just. It would be wise to add about 1/4" to 5/16" to the fork stop at the frame to prevent a pinch point at the tank, especially hard on the hands in the event of the wrong type of get-off.
The net result is about two inches lower at the bar grips. That is a result of the riser being about an inch lower but also angled downward about five degrees, netting about two inches at the grip.