Nitro cat on a modifed engine and 1,000lb less weight... this should be well deep into the 8s. It all depends on what shot they're running and how beefed up the internals are. They say, "stock block, stock appearing blower." Key word is "appearing." It's likely a ported blower with a beefy nitrous shot and updated pistons, rods, super dampener, and a Holley EFI upgrade, at a minimum.
Cool build, but I think they started with the wrong donor car. Hopefully it was a wrecker/salvage, as that thing used to be a fully loaded car judging by the front fascia's lower grille missing the speed sensitive cruise radar module. Coulda built the engine for the cost difference between that and a base model Hellcat.
As for street legal? Not with those tires and the nitrous.