Any squares with over 150k on original engine?

[cadillac_al]

Back in the 70's I always figured most Chevy engines were almost worn out shortly after 100k miles. My 76 GMC has 60,000 miles on odometer which I assume is 160,000 but how can this engine still be running so good? The guy I bought it from was the 2nd owner who bought it from his uncle the original owner. He was a barber that used it to haul his camper.

The 2nd owner that I bought it from put a new cam and aluminum heads and intake and oil pump but he said he didn't touch the bearings. I guess the new heads would make it run pretty good and not use too much oil but I am having a hard time believing the original engine can go this far, especially hauling a camper from time to time in it's early life. I checked the deck surface and the vin matches the truck. It doesn't smoke or use much oil either. Has anybody else gotten a lot of miles out of their old square's original engine?