Only one rule absolutely cast in granite:
One hundred percent of the cars drive line had to originate on a Chrysler assembly line, OR be an exact, direct replacement.
Call it the Rockauto rule. If you can't order it from there, it can't be used.
That said, you can do ANYTHING you choose to do with those parts. No limit to the extent of modification.
Also, the minimum weight. Has to be heavy enough so that there is no advantage to lightweight stuff on the car itself.
We could call it SSS, or Super Stock Slant.
The idea is to make a class where the thinkers and innovators can really go nuts, but keep it basic enough that everybody has a shot at winning