pre-96 8 1/4s will be the correct 27 spline for the old rears. if you can't turn the wheels in the mud, but can take the cover off..do that and see if you can see some springs in the middle of the unit.

Dakotas, Cherokees, some small duty Rams will have the 8 1/4 in them. old Diplomats and Gran Furys, Fifth Ave's as well.

the key is the pre 96. newer will have 29 splines.

Once you get that, you'll need the pre-76 Race/carrier bearings which press on each end of the unit. I believe the newer ones are larger.