valve seats

Are you asking about replacing valve SEATS or valve SEALS?

possibly both I will see once I get into it

Replacing valve seats is a job requiring specialized tools and experience. It is normally done by an automotive machine shop but is seldom required as part of normal valve refurbishment. It is not commonly required.

Valve guide wear can be checked (sort of, using a wobble test and a dial indicator) and valve seals can normally be replaced (with some difficulty, by using shop air pressure to hold the valve) without removing the cylinder head but is not normally worth the effort since any seal failure is probably due to valve guide wear. New valve seals should be part of any valve job as is valve seat resurfacing by grinding.