Not sure what Happened, but here ya go....
I tried to post this as new thread, but somehow it ended up as reply to one of my own threads, totally unrelated. ???
Anyway, Burned exhaust valve. Cast iron seat, Stainless valve, leaded fuel.
Low compression engine (~8.5-1). Compression on that cylinder was 41. Should have been at least 70, the others were 75+. Leakdown proved it to be exhaust valve.
I have an idea as to the cause. But I want to hear from someone else.
I'll post the findings as soon as I find them.