Hi Bigfooter,
The Jag uses, er, Jag parts.
Not trying to be a smart a$$ - here's the scoop:
The Jag differential is nearly exactly a Dana 44. What makes it different is that is uses slightly larger bolts for the ring gear, so a Dana 44 ring gear is not a drop-in. Almost. Apparently some machining can solve that problem.
Since there are lots of 3.73s (I think that's the ratio or very close to it) in stock Jags, that'd be the easiest swap.
Go to
Randy's Ring & Pinion and get all the info, and maybe even some parts!
Tom