A.J. Foyt, Roger McCluskey, Bobby Allison, Denis (Denny) Hulme, Emerson Fittipaldi, Gordon Johncock, Richard Petty, Peter Revson, George Follmer, David Pearson, Mark Donohue and Bobby Unser.
This photo from the LA Times shows drivers the day before the first IROC at Riverside International Raceway, California which was on October 27, 1973. The event was 30 laps of the 2.5 mile road course.
IROC ("International" Race of Champions) was an American spec car racing series for invited drivers that used the Porsche Carrera RSR in its first year. The series went on to use the Camaro from 1975 to 1989. Over the years competition moved from road circuits to ovals, until the last IROC series in 2006. RIR closed in 1989.