Yeah I noticed that in the tear down for the new 3DS that's why I'd willing to believe that a screen work for all of them but I wasn't sure.
I think the old 3DS XL screens wouldn't support the face tracking 3D due to lacking the configurable parallax barrier that the n3DS uses with face tracking, so I'm not sure what would happen even if you could connect an o3DS screen to a n3DS. Maybe the face tracking just wouldn't work or maybe it would even cause the console to crash as it tries to initialize the parallax barrier.
The eBay link hundshamer posted is a used original Nintendo part, which is what you want, the quality of 3rd party chinese parts is inferior. I doubt they are even making 3rd party ones for the n3DS yet.
If you're lucky, it'll be an IPS screen (which have better viewing angles and color) but there's no way to know until you receive it.
The price is rather high for what it is though. You could probably buy an entirely new n3DS XL, take the top screen out of it and sell all the other parts separately and actually make money from it. The parts individually are probably worth more than the console itself.