LSD - Sierra diff - which one ?

I've read several topics regarding sierra lsd, sourced from 4x4, 2.0L - 2.8L - 2.9L models, and that lsd was an optional extra on these models.
Does anyone have any ideas please, diff casing number, part numbers etc.

All Sierra XR4x4s, and the 2.9 GLS/Ghia 4x4s had them too. Stick your head under the arse of one of these and you'll find one lurking behind the output shaft oil leaks