Was it a shop that normally does 500s? It would be easy for someone to think that inserts go there. Also, its common for shops to bead blast heads prior to working on them. So there may be a breakdown in communicatoins. Some would say you should have pointed out to them the need for masking that area.
My $ .02:
Photgraph it all as you have done. Tell them about it. Run it and say if it don't work you expect them to help out on the rebuild.
Personally I think it would be fine, as Terry's experience points out. But you need to go on record.
Lots of things should or should not be done, but they work anyway, been my experience.