I can believe it, just think of what people were doing with full suspension 2800 lb fox bodys and stock long block (gt40headed) with full bolt ons and wild ass cam shafts and 4.56 gears 10.xx
Has the engine been rebuilt/blueprinted/etc.? There's a lot of things people can get away with using "stock components" and no head porting, look at the stock eliminator type guys. There's a guy on LS1tech (GIZMO) who's done some pretty impressive things with a "stock" and "cam only" LT1 for stock eliminator-type classes. I see this LS1 being legit.
You know that car is working right with a 9.98 at 132mph.