Yes, the Salisbury is the heavy duty one.
They have a very robust four pin diff in them, and the shafts aren't bad either. However, they are too heavy and too bulky. They are a divil to service too, as you need to stretch the case to get the diff out. The cases also bend more easily than than a standard Rover type axle. They are way expensive to get aftermarket parts for.
Basically, stick with a standard case and uprate the internals if required!
On a permenant 4x4 system the Salisbury is, to be blunt, a waste of time - both axles take equal torque. They were a hang-up from the old part-time 4x4 days when the rear axle was the only one taking drive until the 4x4 system was engaged. This put a a lot of load on the axle and could cause issues with the 'lighter duty' axle. Once that was removed from the equation the fitment of Salisburys was largely historic - to fit a lighter axle would have been seen to be a retro step (despite offering no performance advantage and costing more).
We had a Salisbury on the racer and we wanted shot of it. I've got a Salisbury on the daily drive and, given the money, I'd get shot of that, too.
If you've got a Series - fit a Salisbury, if you got a 90/110/Defender - don't bother!
Cheers
Eeyore
