The coil pack is a bitch to remove, and this time I tried and failed to do so. Instead I just moved it out of the way as best I could--discovering, in the process, that a ground strap is mis-placed, keeping me from moving the wiring harness as much as I should be able to--and managed to replace all the plugs without having to take it out.
The sticking point is the plug that connects the coil pack to the rest of the truck, electrically. That plug will not come off.
Anyway, the plugs themselves were indeed in need of replacement. #1 and #3 were the least worn, and their center electrodes had a distinctly beveled appearance. #2 and #5 were very worn, and #4 and #6 were somewhere in between. (IIRC, naturally, since I didn't keep them in any particular order.)
Very little carbon on any of them, which is consistent with the "minor head crack" theory. Whenever coolant can get into the combustion chambers it washes the carbon right out, and I know that the Jeep uses some coolant (a quart or so every thousand miles). In fact I'll need to top that up no later than tomorrow because the reservoir is down to the bottom mark, but otherwise I think we're in good shape.
As I've said before this truck has the head that was affected by that defect, and it's going to take some research to find out which head I need...and some serious dough to buy one, even a bare one or a rebuildable core. Actually replacing the cylinder head is probably a weekend job, and decidedly not beyond my capabilities, but it would be a job and I'd probably want to take a vacation day in addition to my regular weekend to ensure I could get it done.
That, however, is beyond my capabilities at present. I need to get on sound fiscal footing before I can even consider a project of that scale. But Jeeps, in general, are capable of going quite a distance; my late sister and her husband drove their '86 Cherokee somewhere well north of 250,000 miles, and the only reason it was retired was because of rust, and the state of Maine said it was no longer roadworthy. This kind of longevity is typical for Cherokees; generally the bodies crap out long before the mechanicals do.
Well, that's the first chore of the day done. Now I have to go cut the grass.