Awesome mod, this turns the Barstow from ungainly in my eyes to beautiful. This is what the car should've looked like all along. My only complaints are that there's a hole in the mesh in the interior and that there's no premade configuration for this variant.
To say that this is a good mod would be a bit disingenuous, as this is just about on-par with dev-quality content. However, my only real complaint would be how much the roof slopes down toward the rear window, which is especially apparent when this is compared to a photo of an actual Mustang coupe. Other than that, and the rear spoiler not actually attaching to the trunk's jbeam, good job!