Do the Glove test in the other post, Head gasket issue?
it will tell you instantly if head gasket....or cracked head is an issue, and it is FREE.
That will either tell you you have a head gasket issue or you don't.
Then you can look at other issues if you don't.
If test show head gasket issue then you will be replacing most of the upper gaskets and may find your oil leak.
4.0l OHV had tendency for head to crack between valve seats, IF overheated, never seen one crack if not overheated, so cracked head is caused by low coolant level and over heating from something else.
Coolant rarely gets to oil passage with a blown head gasket, it can just not having coolant in the oil doesn't mean anything really, as far as head gasket.
Engine cooling system has no internal pressure when cold, water pump is not really a "pump" it is a coolant circulator, like a fan in your living room circulates air but doesn't pressurize the house it is in.
If you remove the rad cap and fill cold engine with water(for now), remove 1 heater hose end, while filling, to get all the air out, then reattach.
Start engine, rad cap still off
A little water may come out the cap opening on startup but then drop back down.
If water keeps coming out cap opening then pressure is coming into the cooling system.
Only source of pressure is a cylinder, 150psi when cranking 1,000psi when running.
That pressure is coming into a head and pushing the water out of the way, it is pushed out the rad cap opening.
Glove test shows the same thing, pressure from cylinder is leaking into the head and adding pressure to cooling system, glove bounces with that pressure.
The cooling systems main purpose is to cool the upper cylinders and heads because when they "fire" it is 1,500degF inside
So each cylinder is surrounded by coolant and coolant passages.
The head gasket has a metal ring for each cylinder, when installed this metal ring is compressed by head bolt pressure and becomes part of the cylinder.
Because this metal ring needs to be compressed it is a softer metal than the rest of the cylinder/piston.valves, so it is a weak point.
If coolant level gets low(a leak) head looses coolant first as the high point and engine starts to over heat, the metal in the head starts to expand from the extra heat, since head is held in place by head bolts it can only expand down toward the block, with head gasket in between the metal ring is compressed even more, this can cause it to fail, blown head gasket.
The breach in the metal ring causes cylinder pressure, 1,000psi, to push out between the block and head into the weaker head gasket material, since each cylinder is surrounded by cooling passages it will breach a cool passage.
The leaking pressure then pushes into cooling system displacing coolant and causing even more over heating since the "air" from the cylinder leak doesn't flow well in the head to cool it down.
The breach in the head gasket could expand more and push thru to an oil passage, when that happens coolant passage and oil passage are now connected and coolant can get into the oil.
The "white smoke" is caused by coolant be sucked or pushed in to the cylinder, with the breached metal ring, on its intake stroke, coolant is then burned when cylinder fires, so has appearance of steam in the exhaust.
This white smoke will smell sweet like coolant, very distinctive odor.