The cheapest way to get taller gearing is fit larger tyres. 255/85-16s should fit with only a slight cut and shut to the exhaust. 35's need more work.
Swapping diff ratios gets expensive. Especially for a salisbury.
I assume you already have 0.996:1 T-case high range already?
??? AFAIK the tallest ratio available for the Sals/D60 is 3.54:1. The SD1 has rover diffs in 3.08:1 and 2.8:1, but that is no help if you can't get a matching rear.

