To complete the final class A class easily go to restart the game The car body design that you had used for the A class races is the same and not back to normal All the parts accessories wheels shape and body parts are all the higher class parts If you made a good car and want to use it in C class you can Do A class then start a new game do not close the game and open it again or you will just get the standard items You will get the same shape car you had previously but the performance will be different