Definitely 1inch, as I tried my inch socket and it went on and was a very snug fit.
As for how tight it was, it was very FT, more than 250ft lbs but doable with my Snap torque wrench (about 1m long)
This diff was clamped in a vice but when doing my 1996 disco, the 24mm nylock nut came off with about 120nm from a air ratchet and I just had the wheels on the ground to stop it turning.
Another way of doing it is to get somebody to sit inside with the foot on the brakes, this should stop the axle turning enough to get the nut undone.