First, I have driven my '64Dog for around 100K miles and always used unleaded gas, as it was the only kind of gas available. I have never had the exhaust valves close the clearance with my mechanical lifters. SO, from my own personal experience I have not had seats destroyed. That's with stock cam stock springs.

HOWEVER,

RR has said he's installing larger exhaust valves. That means the exhaust seat areas will have machine work done on them to fit the larger valves.

It only makes sense, as the head is already in the machine shop with work being done to the exhaust seats, to install hardened exhaust seats at the same time. It won't add a lot to the total bill and it should provide trouble-free service no matter how big a spring he puts on the valve.

R.