90/range rover back axle

Depends on the ages really....

Earlier RRC axles have one shock absorber mount facing forwards and the other to the rear (pre-1989 IIRC), even earlier axles (pre-1984 IIRC) have imperial fittings.

The RRC axle has a different half shaft set up (better IMHO) with the half shaft permanently attached to the drive flange. (Unlike the 90 where it's not supposed to be but often is :-))

Both axles may have different diffs/half shaft splines with the RRC less likely to have 24 spline than the 90 axle.

If you use the complete axle (case,diff,half shafts, wheel hub, brake calipers etc....) then, shock absorber mounts allowing, they are interchangeable.

cheers

Dave W.