I have a detroit in the rear - a very easy installation (you cannot put them in the front as the 101 is constant all wheel drive) and I have a sals ARB in the front. Because of the larger axles in a 101 over other Landies, the ARB side gears are too small for the axles so you either have to get new side gears made (a local 101 supplier made up some on receipt of a bulk order) or you get the axle hole in the arb side gears enlarged. Being in the US you have easy access to Dyna diffs (basically the same as the Sals) so some of their side gears will most likely fit.
I had heard that Eaton had stopped making the 101 Detroit but sellers in the US (Lucky8, Rovertracks and others) still had some in their stocks so you might still be lucky if your quick. ARB still make the 110 Defender/Series 3 locker for the sals diff but maybe not sold in the US. They are made in Melbourne so if you want one maybe check here - be warned though, even though the lockers are made in Australia, it is cheaper for an Aussie to buy lockers in the US and ship back here - in fact cost is 1/2 to 2/3 of the aussie price.
On my way to a camping trip.
My 101 is an Australian Army Rapier Missile Tractor basically still as used by the Australian Army where I assume yours is an ex Brit Gun Tractor.
We have an ex Brit here who imports 101s (he made the ARB side gears) but other than that the place to look for spares is Ebay UK, and most of the Landrover Suppliers such as Craddocks, Dunsfolds etc carry 101 parts - though many are common with other landrovers. The 101 Club in the UK (
http://www.101club.org/) also have cost competitive parts but prompt service is not one of their strong points. They have an online forum as well.
I hope this helps.
Cheers
Garry
