It appears to me that the difference lies in the model year. Through '85, the diff used the four bolt mounting and the diff was the load bearing member and attached directly to the differential mount.

From '86 forward, the new rubber mounts were utilized and the subframe was the load bearing member and attached directly to the differential mount.

The diff in the SD is currently a 2.88 (from an '85) but it certainly will not exchange with the diff in the SDL.........also a 2.88.

So, you fellows need to be careful on the model year, AFAIK.........it's got to be 1985 or before.