Regulations in place at the time limited the team to using elements of production Corvettes .
Pratt & Miller and GM used heavily modified road car mules to test out the engine and other equipment that the racing cars were to use .
Since regulations in place at the time limited the team to using elements of production Corvettes , Pratt & Miller and GM used heavily modified road car mules to test out the engine and other equipment that the racing cars were to use .