It wasn’t a rebuild and it was a used head so what break in would really be needed?
The oil change thing is pure BS and a shops excuse to not fix their mistakes. I personally wouldn’t have let them have the car ever again.
I actually picked up my motor from the shop after they tore down my motor and one of my heads and asked if my car was tuned. I said yes it is JHM tuned and they immediately had something to say about JHM and the tune was a possible cause of my bad valve stem seals! I was really annoyed by the comments and told them not to touch another thing. I picked the bitch up and rebuilt the heads myself.