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I always add this when talking about valve seats. DON'T PUT HARDENED SEATS IN A PACKARD INLINE BLOCK. It's a high nickel casting more akin to cast steel than cast iron. Adding valve seats helps the machine shop and if they fail will continue to help it. Worried about valve seat erosion? Run Stainless Steel Valves. All told that's a relatively affordable option to seats and they're not going to fail.
From seeing many engines come and go through a machine shop and having first-and experience with machining, I'm going to respectfully disagree with the above statement.
1. The Packard block cast iron alloy is not appreciably harder than other makes cast iron. This urban legend comes up in most antique car web sites. We've had Hudson, Studebaker, Oldsmobile and many other old makes quote the same misinformation; many actually disappointed we aren't going to charge them more to bore and hone their "high nickel" block.
2. Stainless valves will not protect the exhaust valve seats against erosion. How long the valve seats will hold up depends mostly on how many highway miles the engine sees. A hobby car getting only a few hundred miles a year will probably last forever. One which is used for long distance touring eventually needs hard exhaust seats.
3. Properly installed hard exhaust seats in a properly tuned engine aren't likely to fail. The only time I've ever seen a problem is when incorrect ignition advance, clogged radiator or stuck thermostat, caused severe overheating to the point everything on the top end was damaged.
Your opinions and results may vary.
jack vines
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