The rule insisting on using the "factory/showroom" suspension design ended with the downsized cars in 1981. But a lot of the early downsized cars' chassis were cut down from earlier ones, as the more modestly funded teams waited on the big dogs to sort out which chassis layout was best. It's probably a toss up when it comes to the earliest downsized Mopars, but if I were guessing I'd go with a cut-down longitudinal torsion bar front/leaf spring rear setup. Petty was the last bucks-up racer running a Mopar, after he switched he sold off a lot of his stuff to the other racers.