I never did finish that rear wheel. I put that particular part of the project on the back burner when I found that in New Zealand any mods (other that labelled XZ550 parts) need a compliance certificate at well over $1000.
I'm now rocking stock brakes front and rear, but powder coated, rebuilt (new pistons, seals, pins, MC kit), Brembo ceramic pads, EBC rotors and HEL Stainless Braided lines. All within the rules and as good as I'll get without signoff from a registered engineer.