[earthquake68]

Very true. Even if you had the early, "soft" valve seats, you won't drive it enough for it to matter. I have a '67 Impala with the original 283 and soft seats. It hasn't had leaded gas in it for 25 years and it still runs fine. After all these years, it just puffs a little smoke on start up. .....which is valve guides, ....not the seats. .........and an inherent 283 problem, regardless.

The first year for case hardened seats is 1974 or '75. If you car doesn't have the original engine, I can almost guarantee it has hardened valve seats.

.....and to answer your question, NO. You can't tell if an old set of heads has hardened seats installed by looking at it. You have to tear down the engine and physically look at the seats and valves in the engine to see if they were replaced.

The bigger engine killer is alcohol in the gas. The old carburetors DO NOT like having alcohol in them. An aftermarket carburetor like Holley or Edelbrock have more modern materials inside them and can take the alcohol a little better. Try to stay away from alcohol in gasoline whenever you fill up.