The homologation modifications included rear wheel wells that were deepened inboard by 1 inch to accommodate larger racing wheels and tyres, a reverse bonnet scoop to allow the race car engines to draw cool air from the base of the windscreen, twin electric fans that were switchable from the dash (replacing the single engine-driven fan), a front shocker tower brace ("K brace") that stiffened the front end, an idler arm brace, and an aero package including a rear "blade" spoiler (similar to that used on the 2-door Holden Torana A9X) and a front air dam. The 13 cars were available in standard body and interior colours and retained the side trim strips, dummy rear brake scoops and unpainted chrome bumpers of the standard GS hardtops. The race cars did complete the 1977 Endurance Series in their new specification and then participated in the 1978 ATCC season.
The homologation modifications included deepened rear wheel wells by one inch for larger racing wheels and tyres, a reverse hood scoop to draw cool air from the base of the windscreen, switchable twin electric fans (replacing the single engine-driven fan), an "K" brace to stiffen the front end, an idler arm brace, and an aerodynamic package with a rear spoiler blade similar to that on the 2-door Holden Torana A9X and a front air dam. The 13 cars were available in standard body and interior colors and retained side trim strips, dummy rear brake scoops, and unpainted chrome bumpers from the standard GS hardtops. These race cars competed in the 1977 Endurance Series and then participated in the 1978 ATCC season.