Production cars 20 or so years ago used to be limited to VIN in some respect. A good example of was a ruling that the Yenko Stinger Corvair had to have been blessed by Don Yenko himself. No copies of a Yenko were allowed to compete. Today most Prod or GT cars are mere silhouettes of the actual car. (rules creep)
But this sure makes racing more affordable. The same goes for IT. Finding the right body/drivetrain combos
is much harder to do than just putting one together that meets the ITCS specs. The VIN belongs only in the SS classes. My opinion .

Tim