Topspeed.com has speculative renderings of each car, with guesses on what Ford might do with each model. Topspeed's guess at new Bullitt showed it as mostly a styling exercise, with a revised front fascia, a blacked-out grille, a vented hood, charcoal wheels, rear 3/4 window slats, and a Dark Highland Green paint job.
For the Mach 1, the rendering imagines an updated version of the 1971-1973 car. There are NACA ducts in the hood, black graphics, rectangular lights mounted in the grille, a more aggressive front fascia, and a black rear spoiler.
To be clear, these are just renderings from one Web site. Neither car has been rumored about in the Mustang community or hinted about by Ford itself. But it's fun to dream, especially with Photoshop and other artistic tools.