blackwolf wrote:

At the time the P38 diff was selected for the rear is was the cheapest 4-gear diff that LR had available off the shelf, that is the only reason. The 4-gear Rover pattern diff, later used in (some) front axles, came along later, and LR clearly decided that changing the design to use that would not be cost-effective.

Sadly as far as I can determine there is no rear axle case available which will accept a Rover diff and fit a disk-braked TD5 or Puma 110 or 130, you'd have to modify an axle case to suit. Furthermore you'd then need a custom propshaft (certainly on the Puma, not sure about the TD5) so it really isn't simple nor cheap.

Although the P38 diff is widely criticised a survey recently on the forum suggested that very few people have found it problematic in normal use, so it really isn't worth the effort of re-engineering the back axle unless you need extreme performance.

As above

The P38 rear diff and axle casing is much much simpler to maintain and set up compared to the Salisbury axle. The latter being reputedly a much stronger axle, but I have yet to see any evidence of that. The P38 axle/diff is meant to be weak, but there appears to be little evidence of that either. A lot of internet hearsay and no real substance.

The other good thing about the shorter diff housing used on P38 equipped vehicles is that the angle of the prop at full droop is less than with the shorter Salisbury propshaft. Quite possibly that means there is less stress on the P38 propshaft UJs. Possibly.

You can... fit a Rover diff centre (not crown, pinion or housing) into a P38 diff with the Ashcroft spacer ring. Before having a dedicated P38 ATB they used to fit the Rover version with the spacer ring into the P38 diff. So you could do it that way around, but not P38 into a Rover.