I have to agree with Cab. Lead was added to supposedly protect the exhaust vales from burning and the valves and seats from excessive wear. With the demise of leaded fuel came the need for hardened seats. However, with that being said, I have run several sets of iron heads for years without significant wear. If I were to build an engine for long term road use, I would use hard seats. To the O.P., don't worry about lead substitutes with your heads, they already have hard seats.