There should be a tag on the rear diff to tell you what diff you have and the gearing. Though I do know if you have a Dana 44 the drain plug is a solid metal threaded plug. The 30 and 35 have a rubber drain plug. As far as the gearing goes, if there is no tag on the diff: Jack up your jeep so both rear wheels are off the ground. Spin the rear wheel one full rotation and count the amount of times the driveshaft rotates. That is the gearing. Most Dana 44's a 3.73 or 4.10 unless re geared at some point. And the Dana 30 and 35 I'm not sure of, but probably in the 3.4 or less.