To be honest about the hardened exhaust seat subject, I have heard different ideas on this subject. Some say that the valves won't last running unleaded fuel. Others say that unless you are running the engine extremely hard for long periods of time ( like a work hauling heavy loads) to create a lot of heat around the exhaust valve they will be fine without hardened seats. I have a set of small block heads I thought about having hardened seats put in. Since this was brought in your thread yesterday I called my machinist and asked him. He told if I wanted them put in he would do it, but then said he didn't think I really needed them and to save my money for other parts.