70 440HP heads

[coronet66jj]

so does that mean hardened seats on just the exhaust side, or both intake and exhaust?

just on the exhaust valve . please note that this is precision work and not to be done on the cheap because if one of the seats were to come loose at very least you could destroy the head ,at high rpm.s. also consider that we have not had any lead in gas since the late 1980's that means that most engines have been running without the benefit of lead as a lubricant since then. ask any auto machinist if it is really a problem, those guys see first hand what goes on inside an engine. better to trust areal pro.