It's fairly easy. I didn't have any experience with the diff before, but I swapped mine out with s15 helical with no problem. You need these parts.
- Side seals- Gasket- Breather valve- Diff fluid
Procedure is failry simple. Drain the fluid, undo output shafts, input shaft, 4 nuts on the back and 2 main bolts under the diff. You don't have to remove rear sway bar. One thing that you have to be careful is shims on both sides. What goes out, come in to the same place. I had to use floor jack to lift the diff when install. There was no way I can lift it up on my back. That was about it. There's some articles out there, so you can search. Here's my write up.
zerothread?id=245320
P.S.: Have you thought about s15 helical? It's a good upgrade.