66 Dart GT HT Whatsitgonnabe?

moparmat2000 said

What year is the castings? When everything went unleaded fuel in the states around 1977 i think the seat areas were locally hardened for the no lead fuel. Trucks didnt require unleaded fuel till 1979, but i would imagine they would have treated all the heads the same way on manufacturing.

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I imagine that hardened zone is rather thin and the seats where the guides are completely worn out need to be milled down at least 0.040".

Since hardened inserts are available for $3.50, I'm thinking I might as well put some in when they are up in the mill and not get the valves sunk in the head either.

I suppose they are shrink fit? Just heat the head up and hold the inserts in place until they heat up, I guess?