There are two different size u-joints in '96 XJ's front Dana 30 axle.

Spicer #260X is the small one (Standard Dana 30 size), 297X are the larger ones (Dana 44 size). There is a tag on the diff cover with the axle build code/bill of materials #. A dealer that carries Spicer can cross the number and be sure of the part he is selling you is correct. You could also bring the old ones in to your local parts store to match them up.

If you have to replace the halfshafts, order the larger u-jointed ones, they will interchange perfectly as a unit. '97 and up all use the larger u-joints. TJ and ZJ shafts will interchange, too. You can also get super strength Chrome Moly halfshafts from aftermarket suppliers.

I've had very good luck ordering gears and other axle parts from these guys:
http://completeoffroad.com/