Unless the Jeep has had minimal maintenance done to it (or it was driven for a prolonged period with coolant in oil due to a bad head gasket or cracked head), I highly doubt the piston rings are bad. I've seen multiple unopened 4.0 engines with 250 000+ miles with perfect compressions on every cylinder. It's not uncommon to see these things reach over 300k miles with regular oil changes and tune ups and still check good in smog tests and have decent compressions.
Go get the head tested/ measured at a machine shop if it has leaks or not. If no leaks, get the bottom shaved straight, valve seats and stems done, get a new head gasket, new intake/ exhaust manifold gaskets, new header (you're gonna need one anyways), and enjoy another 145k miles of life from your engine if the piston rings are ok.
1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...
1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***