As so often happens, I was looking for images for another event but came across a couple of pictures that demonstrate that a 1968 Camaro Z28 RS was used as the pace car for the SCCA Marlboro Cup races held at Marlboro Speedway in Upper Marlboro, Maryland on Sunday, September 22, 1968. There are many races in a national SCCA event like this featuring many different classes of racecars, so the Z28 was probably used as a pace car multiple times that day.
Notice that there are two "pace car" flags attached to the back of the car. While it is hard to tell if it has the Rally Stripes it does seem to be equipped with the larger 15" Rally Wheels. In addition, the Rally Sport grill lacks "SS" identification. This leads me to believe it is a Z28, although it does not seem to have the optional spoiler package or front bumper guards.
Click on the following links to see larger versions of the two photos:
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https://marlborospeedway.org/?page_id=388#gallery/e247143afb500353fca08ee0ab395fca/5383)
https://marlborospeedway.org/?page_id=388#gallery/e247143afb500353fca08ee0ab395fca/541
