I disagree with the statement that you don't need hardened seats on the old heads. When I bought my 68 340-s, the PO had already rebuilt the engine. He didn't install hardened seats. Within a few months, the engine started running rough. When I took off the rocker arms, the exhaust valve on #7 was sticking 1/4" higher than the intake valve stem. The seat had been completely destroyed from the valve beating on it. I had hardened seats put in it and it was fine for many years.
It doesn't matter how hard your valves are when the seat is what takes the ****. It's the seat material that matters. It is the "weak link" in the system.
Say what you want about the hardened seats. If you choose not to use them, that is up to you. From my experience, I use them. You know the risks, make your own decision. Live with the consequences...
