I would imagine that you'll have to obtain a Marti report to get the answer to your basic question. The A, B, C, and D Sports Special packages included escalating level of equipment (tires, trim, handling package, Decor package, etc.) which did not include a bench seat.
My car is also an SS. I was told that the dealer installed the rockers. Don't know for sure. If it makes your car worth more it's to late for me because i changed my dash to XR7 and added eliminator spoilers and hood scoop.