What can be put in the factory housing - a rebuilt Positractionn, a new Torsen, or what? Don't need the ratio changed, nor looking for a "dragster locker", I just want the wet weather/ice advantage of the limited slip rear.

What's the most cost effective way to do this?

What interchange rears can fit - if I get a "lo-mile Junkyard" rear?

Thanks!

Your car most likely has a 7.5" rear axle in it. Rear axle assemblies from GM B-body cars between 1977 and 1996 will directly bolt in if they're the same size as yours (7.5" or 8.5"). You can go with an 8.5" axle, but you're looking at shortening the driveshaft 1" (or obtaining a fitting driveshaft from the donor vehicle, provided it has the same transmission as yours) if you go from 7.5" to 8.5". You're also looking at different wheels for the back due to bolt pattern size (unless yours is a wagon, it's likely to be 5-on-4.75" and the 8.5" is going to be 5-on-5". Wagons are 5-on-5").

You can get posi carriers for either size axle.