Don't forget you need a source of compressed air for the ARB lockers. They do a compressor themselves, but it's extra. Or, if you have one anyway, it'll need to provide somewhere between 70 and 100PSI to operate the lockers. (NO more than that, or you'll destroy the seals!!)
A Two way solenoid valve or tap will be needed too... To supply air to, or vent air from the diff.
They do do the business though, briliant pieces of kit, especialy for the longer vehicles, 109's 110's etc...
Fitting them can be "interesting", especialy if you have a Salisbury/Dana60 axle. You'll need a special tool to stretch the diff' case, also a press for removing/fitting one of the bearings. For the nromal Landy diff's, no problem... A thread cutting tap also (forget the thread and size, but it's not metric) to make a hole for the air line fitting.
It's a lot easier with the axle out of the vehicle if it's a salisbury, the normal diff's you take out and put on the bench anyway....
Have fun... Or more likely, get someone else to do it for you!
Dave B.
109/110 hybrid, Disco 200TDi (yes, it does fit!) with airlocker in the rear.