Finally ... all done! I splashed out in the end, because it's the vehicle I use for 'going where nobody has been for a long time' trips, which if something broke would generally involve a very long walk. It (my trusty 300Tdi) has also still only got 35,000 miles from new, so I decided it was worth investing. Final shopping list ended up being two ATBs, a full set of Ashcroft CVs, shafts and drive members, and after a bit of thought and "what the hell" I ordered a fully built up and pegged P38 rear diff (with an ATB in) from that Mr Barker that pops up on here occasionally. The front was the original 2 pin diff fitted to the vehicle when new, which had broken its 2 pin centre years ago, that was dragged out from under the bench, polished up and I fitted the new ATB centre. Because it's easier in a proper workshop, I wanted them fitted, and I don't have a lot of tinker time, the whole lot was then fitted at a garage a few weeks back.
First impressions - the diffs haven't really been tested in anger yet but I like them. Steering effect is 'noticeable' but just different - and may loosen up with a bit of use. I've just come back from a 300 mile or so trip, most of which was gravel roads and off road, and you just adapt to driving it like you adapt to driving a vehicle with raised suspension where the steering doesn't quite feel the same, and very quickly you don't even think about it except when you get in from another vehicle.
Off road, I haven't tried them in very tough conditions yet but faffing around on steep, loose or undulating slopes, the difference with the ATB is considerable. With diff lock in, it just goes up. Diff lock out, on the sort of grassy incline that would spin a front wheel out almost immediately on a standard vehicle, it still goes up. If you provoke it, the fronts will break traction but they'll work at it, and it almost feels like traction control trying to stop the wheels spinning. Any sort of slope where there is loose rock or undulations that would set off a front wheel spinning (usually followed by the opposite rear) - no problems. Sometimes you hear a slight gear noise (which I assume is the diff centre working) but it carries on with almost no wheelspin at all. I haven't figured out how much differential wheel speed is needed to activate the diff centre but it would appear very little - you never get aggressive wheelspin of the sort that you need to activate ETC for example. Cresting a cross-axle, the sort of thing where opposite corners would unload and spin out, it just doesn't. It's all rather like just having Velcro on the tyres.
So far - I like them a lot, and especially because they're always there and working. It definitely looks like the right choice for 'real world off road use' - I suspect it wouldn't be for trials/competition where half the day is spent with wheels off the ground and a full locker would be superior. Now, an ATB with a full locker also built in ... would go in my Ibex one day
After the late decision on the rear diff, I also now have a spare ATB, and just need to decide what to put it in