The 5 slot "mag" wheels were a common aftermarket wheel style in the 60's and 70's. They were often installed as a dealer option, or by the owner after the fact. You see them on a lot of cars from that era, not just Zs.

anyone familiar with the silver 76 on ebay for 10k? it's up in michigan. not cheap but a nice looking car.

Hmm, in looking at the photos for the car...are the rear bumper over riders on upside down???