This is understandable. Jeep may have soldiered on with the 4.0L engine for a few more years, but for the XJ fans the universe ended in May of 2001. If the revised/improved heads came on-line later than that, they aren't found in ANY Cherokees, so for all practical purposes they don't exist. It is nice to know that there's a viable replacement to be found in junkyards, but as an owner of TWO 2000 Cherokees, it is not a nice feeling to know that I'm driving ticking time bombs and that the only question is "when" (not "if") my heads are going to crack.
I have every confidence in my 0331 head. I don't think its a "when" I think its a "maybe someday possibly if my karma isn't up to par"
There are plenty of 300k mile 0331 heads out there that are just fine. I sure as hell don't think its a question of "when" but rather, "at all".