Originally Posted by JimB

As I understand the rules, you have two options. If your car was available with an option from the factory, you can simply add it. i.e. If the X51 was available as an option in 2002, Shawn could just add it. I think the second option is to "update" the car to a version found later in the series. That's why I run my 99 chassis as a 2004. 2004 had the best available drivetrain so when I converted from a 3.4L to a 3.6L I teched it as a 2004.