I've got a used set of 799 cylinder head coming to me. I plan on putting them on my 6.0L LQ4.

What do I need to replace on the heads?

Do I have to take them to a machine shop to be checked out? If so, what do I want them to check?

I plan on putting new LS6 springs on the heads and new valve seals. What valve seals are recommended?

 

How many miles are on the heads?

You could have them checked for flatness, then milled if they're not flat. You could also have them pressure tested and have the valve guide clearance checked.

 

How many miles on them? If it's not much you can probably just run them.

Or send them to WCCH and have them check for flatness, valve seats, guides, stem height, etc. Go with OEM valve seals.