"How about this beauty at $27,500?"
As I was taught - If you don't have anything good to say... So, I'll say, It hasn't ever seen mud or even sand.
"How do Jeep motors hold up over time?"
As for my jeep - 90 Wrangler (YJ classification), with the 4.2L/258CI motor that was converted to MPFI (multi-port fuel injection - it was carb'd before my time)...
Purchased 6/2011 @ 153K
05/2020 it's at 187K
The straight 6 motor 4.2 / 4.0 is a very popular motor with a long history.
I've never opened the block or had a need to remove the camshaft cover, timing chain cover, oil pan.
I love it's low end torque (great for the trails).
I wish it had more pull heading up the big hills of 70 west of Denver (which is why I've taken your advice and now just take 6).
Once or twice a year it will have a stuck lifter at cold start in the morning (just turn the engine off and re-start and most likely - no loud tick).
It has started to leak at, I believe, the rear main seal. I'll likely tend that fairly easy repair before long.
Mine does burn oil though I do not see "blue smoke" behind me.
Average MPG: 15
I just watched this "stroker rebuild" video, you might find some of the comments worthwhile:
Big Power Jeep Straight Six Stroker Build on a Budget with Newcomer Racing