Not sure if you know this,,,,,,,, but you only typically need harden seats for the exhaust valves.
Only 6 are needed.
Put the seats in ,unless you are planning on not using the cylinder head that long.
Try & tell him to put the shallow seats in, so you will not get into the water jackets.
All the factory alum heads have seats in them, do you think they would be putting in seats if they would fall out?
If you install them correctly, w/enough interference fit ,you will not have any problems.
Goodluck!
