"392" could be the gear ratio - 3.92:1 - and I'd want to make sure it's a ChryCo 9.25. If it is, they aren't bad axles - I seem to recall that they were used in some fairly HP late musclecars alongside the D60 (they got one or the other, natch.)
You'd probably have to do a fair amount of work to make it happen with your XJ - you'll lose some ground clearance (larger differential. The D35 is something like 7-5/8" IIRC,) and you'll probably have to move the spring pads (most pickups tend to be "spring-under", while the XJ is "spring-over".) And, the lug pattern is probably different - meaning either get custom shafts made (alloys with special flanges to get your 5 on 4.5" pattern to match the front) or you'll have to get some conversion for the front (I haven't looked into unit bearings that might fit in place of stock and change the lug pattern. Yet. It's on my list...)
For the amount of work you're likely to do and the money involved, I'd say "Pass". (I just wanted to explain why first.) You can do better finding a Ford 8.8" (later 8.8" axles came with discs OEM, so just get a C-clip eliminator kit,) getting a later 8.25" out from under a 1999-up XJ (29-spline shafts. Get a C-clip eliminator kit for it,) or - if you're really lucky, you can find an XJ/MJ D44 (difference is the orientation of the spring pads) or get an "early Bronco" (the U-100 model, not the Bronco II) 9"/D44 combination - both of which will be much easier than dropping in that 9.25", I'm quite certain.
