I recently saw a Mach I with the sunshade covering the rear windshield. It is just like the camaros' had, but looks much better. I was wondering if anyone new where to get it.
Yeah, those are usually referred to as "louvers". When Ford offered them in the 1970s, they were called "sport slats".
I think there's one company that makes 'em for Mustangs these days. Apparently you have to be careful with the install, and the top louver is differently angled compared to the rest. A search should turn up more info...
Someone here has a red Mach1 with the louvers...looks good to me, but a lot of people don't like 'em.