Either way, it's still a 392.
The Chevrolet Corvette Z06 (C6) is an example of a few cars where it can be modified to resemble another variant. In that case, the ZR1.
Did you check the customisable tail lights?
All Challengers seen in the game, playable and House-aligned ones, are the 392 variants. No new ones are added.
CarCrazedAlex586 wrote: Where would Blackridge be located? Razor visited there so it might be near Rockport.
It doesn't necessarily have to be near Rockport. The airport, although inaccessible, is the only place outside the closed-down road where people can travel outside the city.
Don't forget the Beck Kustoms F132. You can only visually modify it.