well also, running 85 octane probably kept the temp down a bit. I am sure you're right too, high nickel content probably helped with not only strength but also has a higher heat tolerance.

Another thread said something about how when the valves close and open they tear some of the seat off from tiny spot welds. If the block was closer to the relative strength of the valve, i bet you would have less of that.

I didn't ran lead substitute in my first small block. I was running lead in my 273. I just recently pulled apart the first one, valves look fine. I am no longer running lead in my 273.

If i had a rare, expensive, or high output engine that for some reason did not have hardened seats...then i'd run the lead again. But at about an extra 8-10% the cost of a tank of gas for lead substitute, i can pass for the time being.