hmm lets see here young jeeper apprentice. Ignor what altozone and the other store say. there are two pcv valves. Both are on top of you valve cover. If you are leakin from these theres two solutions. pull said pcv valves and clean them out. the other is to walk into a descent autoparts store with the valve(take it off in the parkinglot) walk past the idot counter and walk till you find the pcv valves. they have them but their too dumb to know. That or hit up a local junkyard and grab one wont cost ya but 50 cents max or free at junkyard. make sure its not clogged and there ya go.
THe temp gauge is off how? Do you know for a fact its running hot or cold? THese things normally run around 195-210 degree's stock. If you know for a fact its inaccurate try checking the sending unit, might just be bad or loose connections. That or just go get some aftermarket gauge and mount it up.
Your rear end noise IS your diff. Is it a grinding or wining noise? if its a wining noise your pinion bearings are worn and need fixing. It happens, heck mine wine since i rebuilt my diff. Can't explain it. one day ill fix it.... If its a grinding noise, then well it could be worn, chiped, cracked, gears. Could any of the gears in ur diff. best way to check is to pop the diff and look for metal shavings and spin the axle looking for bad wears or chunks missing.
Last but not least the 4x4 engagement. its really easy. to go from 2wd to 4hi the shifting is on the fly, try and do it at low speeds just to be on the safe side. to get into neutral is just another shift away. To put it in 4lo put it in neutral, shift, put in drive and go. rolling, aka barely moving makes this easy. thats the way to do it, if thats ur x-fer case ya got. if remember right ya got the 231 which is settup 2wd, 4hi,Neutral then 4lo. If not tell us and can we can tell ya how to shift her.
used to have my project jeep.... had to sell her and now i just dream of the future.