Michael,
Sorry for the joking................. but seriously, I actually have one of these windows on my 45 truck.
I can get you measurements if you wish.
I had seriously thought about replacing it with the standard fixed-glass window, because the weatherstriping for the slider is quite unusual, not a typical evenly-sized unit, and I'm not sure available if needed. I decided in the end to run with it, as my weatherstrip is actually quite pliable and complete. And if things ever go south, I'll go back to the standard fixed design.
Interestingly my 1993 Toyota pickup came with what appears to be a very similar window setup. I don't believe it's the same size, however, as my glass man couldn't find a used '93 vintage sliding pane to replace one that came broken on the 45--so we made one out of safety-glass and had it drilled out for the catch. But it's interesting to see how the progression of more modern parts first appears on an older vehicle. From what I can determine, the 45 slider windows were only a factory option at the end of production, on the 1983-1986 longbeds, which of course, we never got over here.
Not running a campershell or canvas rear, the slider really isn't all that necessary, but I agree, it does have that odd-ball/rarity factor.