Your 3.0 Sport has the same rear end as the 3.0 Monteros. Should use ARB locker #RD25. You can also use a factory locker from a '92-'93 Montero SR, which you may find at a local pick & pull. If you go that route, you'll have to change gears because you have 4.636 and the SR's came with 4.625. Not really a significant difference unless you have full time 4wd, which I don't think you do. You also need to be aware that this means you have the large front diff and should be able to fit the new front ARB when it comes out.

Lee
'94 LS, 3.0 V6, Auto, completely stock