The exhaust seats never lasted that long in those motors anyhow and the seat faces are wide originally to help cool the valves. The middle two cylinders have a siamesed exhaust port so two exhaust valves are in close proximity. Never use a WILD cam in these motors or they run awfully at some part of the rev range.. If you could get AVGAS cheap it would help the seats. A lot of race cars ran it at the time. Nev