Good point about the Salisbury axle John ... although I've had about 6 Series LR's they've always been SWB and I kinda forget that 109's aren't always quite the same out back!
If you have Rover axles front & rear (most SWB and some LWB I think) it's a fairly easy but potentially messy job ... remove halfshafts and props then swap the diffs straight over. The 30% gearing change (or thereabouts) is within a gnat's whisker of the increase you get from an overdrive. Thoroughly worthwhile conversion (in my opinion) especially if you've fitted a beefier motor ... one LR I had recently had a TDi, an overdrive AND Rangie diffs ... it simply purred along at 70. I don't do any greenlaning or events though, we just use LR's in the fields & around the holding here. And what John said about towing is especially true ... if you had a standard 2286 Series engine and a heavy trailer, with RR diffs you'd be lucky if you got it out of 2nd gear!
The advantage is that if you're unlucky you can pay £250 for a shagged overdrive ... whereas a pair of diffs ought to be less than £100.
I do have a pair of 3.54:1 Range Rover diffs going spare at the moment (in SW Wales).
