Usefull Mods?!?!
Useful as in performance? Or useful as in "Gosh, Harriett, that thing really looks like a MILITARY type vehicle"!
Performance wise:
-A cold air kit for the engine! Go to Jegs or Summit and get the filter, silicone boots and ell's and pipe for less than the price of a "kit" from one of the "names".
-Headers from a good maker
-A bored out throttle body (better breathing)
-Yella Terra roller rocker arms (about $400.) frees up HP lost through friction
-Free-er flowing exhaust (nothing I've found will make a 4.0 sound like a v-8, but you can gain some HP)
-Then, if you REALLY want to get intimate with your engine...go look at Dino's jeep mods-www.jeep4.0performance.4mg.com- and follow his stroker build-up. The guy SHOULD have charged for the massive amount of info he is giving away for free. He built a killer stroker 4.6L I6 and is giving away all the blood, sweat and tears involved. I know the V-8 guys will say that it won't perform like a bent engine...and it probably won't...but it will have a ton of low end grunt and will run for friggin ever! Dino did his for about HALF the cost of a stroker long block from an aftermarket builder.
For my two bits, I'd make the Jeep perform first, and be able to turn those 35's you're dreaming about. Then check out some of the lift kit makers and start saving! (don't forget Iron Rock Offroad for a lift kit!!! and take a look at the "customer's rides" while you're there...I drool every time)
-Lastly...I don't have a stake in any of the companies or persons I've mentioned. Just think you could do much worse.