Dammit Paul, making us all be considerate and open-minded. Whats wrong with you.
I'm not going to write a novel, as that would probably be difficult to read. Just very broad statements follow:
thez,
Differentials fall into three categories:
1. Open
2. Limited slip
3. Locked
You can make an open diff locked by welding it, which is very cheap.
You don't weld a limited slip or locked diff as they are already driving both wheels.
Chances are you have an open diff at the moment. You can weld your existing diff to make it locked.
If you want a LSD diff, some Subaru diffs will work, but you'd need to do more research on which precise one. Research means search.
I hope my English was understandable. If not, private message me and I'll try to clarify.
Dave