I recently did the same thing and the bits of advice I got from the board were invaluable. The first thing to do, is get 2 new rear main seals from the parts house. Reason being, if you botch the first one, you have a second one ready. Often times, when you install them, it's easy to shave some of the rubber off of them, in which case they won't seal. The next biggest suggestion is get the 3M Weather Strip/Gasket Maker (Gorilla Snot) for sealing your new pan gasket and some permatex high tack gasket sealer. Levy or Ozark gave me that advice and it worked like a champ.
Things I did for ease of access:
Jacked up the rig, put stands under the frame towards the front and removed the tires for ease of access and freedom of movement.
Next thing you will have to do, assuming you have the 258 and have drained the oil and pulled the oil filter, is to put a piece of 2X4 and a jack under the bell housing, jack it up a little to take the weight off of the motor mounts. You will have to remove the passenger side motor mount to get to one of the pan bolts (there is no way around this if you have the I6)
Pull the pan,if it's been a while since it's been down, you may need a rubber mallet to pursuade it to come off. Once off, loosen your oil pump pick up and turn it out of your way. Loosen the rear 3 or 4 bearing caps and remove your rear cap completely. (The reason you do this is to let the crank hang a little at the back... we are talking fractions, just so you can get the seal out of the block)
When replacing the seals, use a little liquid dish soap to install. Replace the seal in the bearing cap. Take a brass punch and tap out the seal that's in the block. (Make sure not to tear up the journal) Once that seal is out, put some soap on the back side of the new seal and a little oil on the crank side of the seal and slide it in. I found that this takes patience and steady pressure not to score any of the rubber off of the new seal. If you do, don't sweat it, just insert it all the way and remove it. You will have lubed the area a little and will now know what you need to do to get the second one you bough in place without tearing it up.
Once that's done, put a tiny amount of silicone on the back side of the bearing cap (behind the seal tranny side), re-torque your bearing caps to specs check all of them front to back. Put your oil pickup back in place and re-torque.
Hopefully you pan doesn't need as much attention as mine did, but make sure it's nice and clean as well as the block side mating surface. Paint the high tack on the block and position your gasket. Use some of the gorilla snot for the front and real seals. Next, put a healthy coat of the gorilla snot around the actual oil pan, heavy at the corners, front and back and then put the pan on. Use a hand held nut driver and tighten the bolts up. Don't over tighten or it will force the front seal out and blow oil everywhere. You just want this hand tight. After 100 miles you will want to retighten them by hand only.
Redo your motor mount and anything else you did for the prep and all should be good.
Good luck and sorry for the length of the post. This is about as step by step as mine was and I appreciated the help from the board. It made it a lot easier.
83CJ7 definitely broken this time