Tom Woods will put whatever sized u-joint in there you want, but I'm gonna have to guess its either a 1310 or 1330 u-joint. A way to find out is to measure it. The cap diameters will be the same on these... (1 and 1/16"), but the width on the 1310 is 3.218 (very close to 3 and 1/4"), while the 1330 is 3.625 (3 and 5/8"). If you're going to buy them at Auto Zone or a parts store like that, buy the Spicer u-joints... they should be like $15 or so (and a tip for buying them there, bring a tape measure and measure them because you will have to say "I need a rear u-joint for a jeep wrangler"). I'm not sure if you've ever messed around with needle bearings, but if you haven't they can be a pain to change on the trails. You might look into just getting another driveshaft (they run around $230 I believe), if your budget can handle it. Also, I'm gonna guess you're running a 35" tire or so on a Dana 35... might want to check upgrading that also. The explorer 8.8 rears are fairly inexpensive and will be cheaper than upgrading a 35 in the long run.
