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.