Deos it run well?
Probally just needs a fresh head gasket. That's really easy on that mill to replace.
The 4.0L is a tough little bitch and easy to rebuild. My 4.0L went through hell. Leaky everything, spun bearings, low oil pressure, etc. etc. You know how most 4x4 have bearings on the fron drive shaft, mine didn't! I could literally lift and turn my front axels by hand. My whole front drive was ground down to nothing. Rattleing, grinding, popping everywhere. Sounded like I had a cheap diff locker.
I drove it from Ocala FL to Gainesville Fl with only 5 psi oil pressure from an offroad "incedent". And when I tore it down,ifound it really only needs rebuilt with new pumps. A hone is needed as well. My cylinders are polished nice and smooth from all the tree bark I found between the piston and cylinder walls. I had someone rebuild the iron head just because I knew someone who would do it for only $50. Tough engine.