The small block Chevy engine in my El Camino went 300,000 miles and never had the heads off. I did replace the timing chain after 200,000 miles but only because I had the water pump off to replace that, and "while I was in there" replaced the fiber gear. It had very little wear and if II had known that I would not have bothered, but I had it apart and the replacement on hand so I replaced it.
I took apart that engine just to see what was worn.
I dropped it all off at the scales to be recycled. I replaced that engine with a factry NEW GM Crate engine with a 24 month or two year warranty, delivered to my driveway for $1,700 all in. I did the engine replacement mostly myself. I did have a buddy come help pull the old engine out and stab the new engine in place. The rest of it I did. I did borrow his engine hoist and engine stand.