If you read the article on the Super Stock cars, it could be purchased from any Plymouth North American Dealer. This means that anyone that could fork up the money could go buy one. It came from hurst with the street tires and low profile oil pan. Once bought, people that would be racing them would put slicks on and change to the deep pan. The buyer would have to sign a disclaimer that the car was sold without warranty and didn't meet Federal Vehicle Safety Standards, but this doesn't mean people didn't drive them on the street.
I would say that if you can buy the car directly from a dealer that it should qualify. It doesn't meet Federal Vehicle Safety Standards, but how many cars of that era did.