Well, I am sure that he must have spent around his asking price to build it, but will probably get 9k realistically. 10 is within reach for this car.
Not You, in this case, it doesn't matter if it's an original GT-S or SR5. If this car was a GT-S, well who cares? It doesn't have the original engine, drivetrain or any of the things that make it an original GT-S, just a VIN number. A GT-S should be valued as such in original condition. Any engine swaps or crazy modifications, it will be valued the same as an SR5 with the same exact mods anyway. It's still the same AE86 chassis. Swapping things out from the GT-S is taking away from what made the car a GT-S in the first place.