the difference lies in what brake rotor you use on it.
If you get one and it doesn't fit, try a 97+ brake rotor.
My D30 has 87 knuckles, with 87 calipers, but has 97 hubs and rotors. mostly because I swapped a 97+ housing to mine and had bad bearings on the old one. So I kept the good bearings with the housing, but swapped the knuckles because I had new calipers for my 87.
It looks like the first link you poasted is for newer wranglers, I'd bet they used the same brake rotor as the late model XJs.
The second link that says from 84-91 would definitly work on your 87 axle.
The difference is in the unit bearing "hat" that sticks out from the mounting surface. As long as you get the rotor with the correct offset in it's hub then you should be able to make it work.