Swaped a newer Engine and transmission into my 89 Ranger and started to disassemble the old engine that had very low oil psi and was letting antifreeze in the oil at 220,000mi.
I have pulled everything from the heads to the pan including the front cover and haven't found an obvious coolant leak? And the one thing I thought for sure I'd find bad was cam bearings but the front one was with in specs and the others look good visually. The oil pump has some slight scoring and nicks but nothing extremely bad and there is a impressive lip at the top of the cylinder wall and lots of oil sludge from the the previous owners maintenance schedule.
I'm going to tear into the crank bearings next that could explain the low oil psi but I still haven't found the source of the coolant leak, it's very obvious it wasn't burning jut going straight into the oil.

 

2.9s are prone to cracked heads. Look at the top surface of the head under the valve covers around the base of the valve spring seats. They tend to crack from the top so they let coolant into the oil but not into the cylinders. Cracks are usually visible to the naked eye without magnafluxing. Worl Products used to make heads for them with thicker castings but they've been discontinued, you may find a used set on eBay or somewhere.

Here are some pics of the heads on my '89 2.9 when I first tore it apart and cleaned it up with some carb cleaner:

 

I haven't cleaned enough sludge off the heads to check for cracks yet, might look at that tonight, did pull connecting rod bearing and one main bearing.

The crank bearings are probably the culprit for the 8/10 lbs of oil psi at 1200 rpm and the oil sump looking like this probably didn't help.

 

Actually that oil pickup doesn't look too bad. I did have a clogged one on my Escort, it was jammed with "coffee grounds" so no holes in the screen were visible, even after soaking in solvent.
It is disappointing that World Products discontinued their 2.9 heads. So there are no aftermarket heads to replace the chronically bad stock units, whereas there's dozens to replace small block heads.