Now you're talking about the Widebody Kit or still the normal body kits?so is that the last amount of body parts except widebody
You'll unlock it if you do enough Outruns in Coal Harbor West area. In the career mode, you'll only get 1 wide body kit and ONLY 1. Once you used it for a particular car, you can't have it for other cars. You'll get an SMS saying that you've won a Unique. That unique IS the WBK. This only applies in CAREER mode.
But once you're done with the career, it'll be available for all the cars in the Quick Race mode.