Sorry to cause any confusion. Any search here for cam/lifter failures will likely cover most of this in great detail.
However, I'll do my best 'jeepxj3'.
SB-Chevy(Gen 1) lifter dia=0.842, SB-Ford(windsor)=0.874, SB-Chrysler(LA)=0.904, AMC/Jeep 4.0=0.904
The AMC/Jeep-Chrysler 4.2(258cid) and 4.0 engine all use Small-Block Chrysler style 0.904" diameter lifters(and probly other AMC engines that I'm not aware of). Often the very same part# is spec'd for ours & the V-8 depending on the mfr. These were the largest(widest) lifters of the 'big-three's' early small block V-8's at the time and offer many benefits to valvetrain performance and durability. The only real drawbacks to this larger diameter are additional weight and cost. This larger dia provides a greater surface area on the face of the lifter for the cam lobes to contact, thus allowing the use of wider cam lobes as well, to distribute the applied loads over a larger area which generally equates to increase load capacity and/or decreased wear for a given scenario. This wider lobe achieves greater leverage on the face of the lifter to initiate rotation of the lifter in its bore. This extra width also permits the lifter to accommodate more aggressive lobe profiles without binding /excessive wear. This is, and has been a major beef of mine (and possibly many others?) with current aftermarket cam options. If you can find one laying around, mic the width of the lobes on a factory cam (or when you take it out). Cast cam lobes will vary in exact spec, but they are generally wide enough to take nearly full advantage of the width of the lifter face. If you've found a nice aftermarket cam choice from any of the big name suppliers, often with great cam profiles, you'll find that the lobe widths are much narrower. In my research into this over the years I have discovered that most of the suppliers for cast cam-blanks (or cam-cores) deliver them with lobes that are essentially a generic SB-chevy width. The lobes & base circles are correct for our engines, but the widths are markedly narrow for our application. I have personally spoken with Crane (whose products i still run), Comp and Lunati. I have also spoken to multiple smaller companies that do custom grinds and have yet to find a source for "quality" factory-width cams in anything other than factory-grinds. Sounds like some of you may have found a supplier? So I have given-up and accepted that to get the cam profiles I prefer, I will likely have to change cam/lifters when nearing the 30k mile mark on THIS engine. Granted, everyone's success and setups are different.
So here's the heart of the matter: Take a drink coaster or a napkin on your coffee/dinner table and place 2-fingers very close together from directly above near the center of the napkin and try to turn/twist it. Certainly, it can be done. Now take those same two fingers and place them further outside near the edges of the same napkin and turn it. Much easier? Flat-tappet lifters must rotate in their bores to wear evenly and to produce any expected service life. The wide factory-style lobes are like having your fingers on the outside of the napkin, narrower aftermarket cam lobes provide reduced-leverage to rotate the lifters like having your fingers more near the center of the napkin. In addition, the bulk, rather ALL of the wear now takes place in a smaller, more focused surface area of the lifter face, where it is the weakest. Take one apart, look inside and its basically a little metal bucket. Highest load bearing ability with the load applied at its most peripheral edges. Constant loading in the center and it will essentially 'cave-in'. I'm now on my 3rd cam in this engine with both prior failures due to a lifter failing to rotate and ultimately wiping a cam lobe. This issue is further accentuated by low zddp oil that is now common, more aggressive cams, higher spring pressures and any underlying valvetrain problems that may exist in ones setup.
In speaking with one of the cam mfr's, it was mentioned that there must be an inherent problem with trying to modify this engine platform, as SBC's operate with this lobe width with "no problem, even with way wilder cams and under much higher valve-spring pressure". True. And argue that how you like, i could only agree given that those cams are paired with a lifter dia that was designed to accommodate it. Employing that width lobe in an engine that has a 7% larger dia lifter is condemning it to early failure. They are mismatched parts. And of course...
*Discalimer: I have no problem with SB-C's or SB-F's. I like anything that runs good!. Especially my hotrod Jeep! I greatly appreciate this forum. Meant no offense to anyone
Disappointed. "IF" a provision were made for this (enlarged push-rod holes) I would be almost delighted to take an afternoon to pull and inspect the lifters for condition/ wear pattern & proper rotation. It would be SO great to be able to replace a ~$50 set of lifters proactively, to maintain a good cam in healthy working condition 
) on the SB-Chevy lobe-width's (< .842), that all the major cam mfr's want to force on us. 
Thanks. Sorry. End of Rant.
