mebe2K..my 1990 had the same symptoms as yours. I got lucky and found a 1990 Ranger with a 4.0 and a junk body. Took out the 2.9 with the cracked heads and installed the 4.0.
Oil pressure is at a steady 40 pounds and more power. Glad I did the swap. My 2.9 was what I called a 10 mile engine. It would run decent for 10 miles then the oil pressure would drop, tick loudly, and run like crap.