Re: hardened valve seats L78
We've put over 17K miles on our L78 car since we bought it. No problems. We had an L30 327 Chevelle with 91K miles on it and the engine had never been apart. No problems there either. High RPM and/or high loads are what most likely to hurt the exhaust seat. Old heads have probably soaked up enough carbon in the seat area that they will be hardened somewhat already. A light touchup will still leave a good seat. The machine shop I use wouldn't guarantee that he wouldn't hit water when machining for the hardened seats. Not a big chance of this, but possible. I'd hate to gamble one of my old heads to find out.
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Chevelleless after 46 years......but we did find a low mileage, six speed, silver 2005 Corvette. It will just have to do for now. 
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