[kipps]

I've got a 1987 with a sliding rear window that looks exactly like that, with the bare aluminum frame. I'm not really sure if it even latches. It stays shut on its own, though. I'm also not sure if that aluminum sliding window is stock, or was a popular aftermarket option back in the day. Either way, it will fit your truck.

I'll be ditching that window at some point in favor of a single solid window. One pane is broken, and I want the better visibility of a solid window.

I have no experience on the vinyl, MIP(I've seen it advertised, but what is it?), and carpet conundrum. I've been told that carpet might actually be better for the metal floor, since it allows the metal to dry out if it gets wet. In contrast, vinyl traps water against the metal, and causes more rust. If you go with vinyl or MIP, definitely paint the floor good, and ideally, use a coating like lizard skin on the floor under the vinyl.