I don't think you will need them unless you plan on a lot of hard use. Its the heat with lack of lubricant that eats away the seat. The lead in fuel was the lubricant. Replace only those that are worn out.
My thoughts are, if you replace all 16, you now have 16 parts that could come loose! To replace these, the machine shop will cut out a area around the seat, then the new seat is pressed into place, no mechanical bond. The next step is to finish machining the seat to spec's. One of the draw backs is if they seat is not matched to the port throat, they leave a step which really messes with the air flow on the intake side. Replacement seats are great way to get a worn head back to full compression, but for long term parade style driving, totally unnessecary! Joe
