Yeah, I just came up with the GT350 thing off the top of my head. I think it would make more sense than having that Shelby GR-1. The Mustang could be a lot cheaper, even if it was $50k.
A price that high would certainly give Ford some room to play with development. Maybe some lighter body panels, a great handling suspension setup(maybe time at the Nurburgring like the Z06), and of course, more power. Although $50k is a lot for a Mustang, it would still be almost $15k less than the Z06.