Great miles. With all your experience, you should be telling us how to verify oil pressure. Old School would just install a cheapo oil pressure gauge. You can look up "leak down" test on Youtube and try that first. You may have to scan for codes. good luck, feed her some fresh oil and stick some stp in there. If the bearings and caps have too much clearance, as well as rings you may need a rebuild. But so what? that would be good money spent on one of those rare vehicles that has made it to "zero velocity" stage to life.
Replace the oil pressure sending unit they usually go out often but it has lasted a long time! Replace that give it a good oil change and clean and tune up everything and it should run nice! Best of Luck!