Appears to be very good quality product. However, unless I missed something, I don't think they'll work with the stock Z900RS handlebars.
Website states: "for 28.6mm handlebars...spacers available for 22mm handlebars".
For us yanks, that translates to 1 1/8 inch or 7/8 inch. The tapered bars on the Z900RS are 1 inch
at the center where they are mounted.
I'm certainly impressed with the quality of the product though.