For anyone who isnt aware, the standard valves he is referring to on his engine are two piece ones with a sodium filling.

The 1 piece steel ones he is referring to are straight 21-4N valves, as opposed to nimonic80 or anything fancy like that as they arent really available (well not for sensible money)

Things to consider are, fairly high rev limit on his engine, like 8Krpm
Lots of heat in his engine, its running lots of boost and will probably be on gas at some point too.