Super Stock drag racing got it's start in the early sixties, and was a very popular class for about a decade, mainly because the cars were the same as the ones you could buy at your local dealer. Sort of.
Factory SS cars were in fact available from the dealership, but they were usually special order only and frequently were stripped out base models. The Plymouth Belvedere pictured here had thin van seats (they were lighter than a bench), no back seat (it's heavy), no heater or air conditioning (it's heavy), no radio (it's not heavy but you can't hear it over the engine anyway), no sound deadening (it's heavy), and no hubcaps (because you're likely to get rid of the wheels anyway). In short, they weren't nice places to be for more than a quarter mile at a time. Modifications were few, and limited mostly to safety equipment.
I have no idea if this Plymouth was a genuine Super Stock car back in the day, but it was very convincing if it's a clone. Everything was correct, and it looked and sounded great.