Interesting sideline to this post.
Back when I was younger I was working as an engine reconditioner.
One of the jobs that came in was a cast iron crossflow falcon head off a taxi running gas.
The valves/seats had been running that hot and dry that it looked like the inlet inserts had fallen out.
No inserts in those heads but fitting some was easy because there was so little to machine out.
We just tidied up the holes and fitted hardened inserts.