yeah osama has it right. I think there is also something different about the axles. I don't think the basic axle is different, just something added to it for the LSD. The LSD tranny also uses different output shaft seals.
a while back I also checked on buying a rebuilt LSD tranny. I was given prices in the range of 650-750 if I remember right. Though they could have been completely on crack, cause when I kept telling em I want the LSD tranny, and would you like the model #... they pretty much ignored me and just kept asking what kind of car I have.