There were a few small differences, I've found from my manuals.

GPZ had BLACK casings, instead of silver.

GPZ had a 10:1 compression ratio versus 9.5 for the KZ

GPZ has an electronic tachometer system versus a gear-driven mechanical one for the KZ.

That last one is the only thing that concerns me. I'll let you know more when I find out more.

-WileyC