Doesn't surprise me that the car was a bit "extra-legal"; that car & Bobby Warren's Camaro were tough to get past in SS/IA back in the day (I own Ed Hamburger's SS/IA Duster, which has some cleverness but not that much), according to the guys I know.
Another really worked-over car is the Hamburger/Bachelder/Chipman Demon, which is still around in Maine.
That Challenger looks great, it's a significant car, and from my perspective, a good deal. I know I'd take that kind of money for my car.