My girlfriend just had her 4.0 pretty much rebuilt and it got me to thinking about changing my rocker arms and lifters. I've never done internal stuff so I don't know ofa reliable site to get stuff Or a good aftermarket company for them.

 

summit racing has some stuff for the 4.0. 2 companies i know of off the top of my head are Harland Sharp, and YellaTera. you got to watch out on which ones you get cuz some of them require machining of the head (milling the stud bosses down) to be able to clear the stock valve cover, so pay attention and expect to pay round $400

 

Links:
http://www.summitracing.com/parts/CSP-S40196/
http://www.jeep4.0performance.4mg.com/valvetrain.html
in the 2nd link, im not sure if crower is still making them, last time i checked i couldnt find them