i have fitted a salisbury axle to my 90 i used a front propshaft from a range rover tdi as its extended and collapsed lengths worked out perfect. it was an inch shorter than my original and the salisbury is an inch longer nose after lots of jacking and compressing the prop was perfect you will need to change the spring locators for original 90 ones but these are cheap. A salisbury axle is extremely heavy! But it is a 4 pin diff very strong shafts are much stronger and 24 spline the only downside it the salisbury diff bango or center is lower to the ground than a rover diff this can be cured by grinding it back bearing in mind the casing in almost an inch thick but i didnt bother i wanted a strong bullet proof axle and thats what i got
Hope this helps
Jai