Front Aussie or similar auto locker fairly easy. I'd never been in my differential before and I've got mine in with 7 or 8 thousand miles under her and no issues. I chickened out on doing the seals.
Hardest part I think was getting carrier out as well as back in. The latter wasn't hard. But it just didn't feel like it was going in right. The locker is one of my favorite mods. Most bang for the buck for improving off road performance in my opinion.
1994 YJ Wrangler, 4.0, AX15, NP231, 35x12.50x15 BFG KM2s, 4" RC lift, 1" lift Boom Shackles, 1" BL, 4.10 gears, 8.8 LSD in rear and D30 Aussie Locker in front, on-board air conversion, Ramsey RE8000 winch.