Salisbury is a completly different axle to a rover axle if you have a rover axle you will need the complete axle.
Then there is modifications to the propshaft if its a 90.
I have a 4 pin Rover diff in Very very good nick. its a bolt in replacement in a rover axle but its not cheap. A salisbury axle and diff internals are far stronger than rover by design and sheer size of components.
Let us know what you currently have if your diff had broken and its a salisbury it will need a rebulld again quite time consuming and costly exercise to do it right.