Be aware that not all 2.5 XJ's have 4.11 gears. My '84 has 3.54 gears, with an auto tranny no less. The gears can run from 3.07 up to 4.11, with 3.54 and 3.73 seeming to be the most common. If you are just hunting for gears, then don't worry about wether the axle is disco/non-disco, they are all the same.