^^^ I'd say those are the first-year IROC ('International Race Of Champions') cars, before their numbers and driver's names were put on. I'm not seeing any safety equipment, either. IROC was short series of races, specifically tailored to the television market (ABC telecasted it), which had a good string of F!, NASCAR and sports car drivers. They drove these fairly stock 911's the first year, but apparently maintaining them got a bit spendy. They switched to Camaros the next year.