How often did they change the oil?
My trusty 1986 El Camino OEM engine went 300,000 miles before it was worn out. Mostly the valve guides causing smoke from the tailpipe.
It was not pristine, but 24 years of real world driving in sub zero temps to 100+ degree days on a highway trip it ran fine. And the new 350 replacement brand new crate engine was $1,700 delivered to my door.
All on conventional oil, with regular oil changes.