With that countersunk pattern in the lugs and the location of the crack, what about the possibility of it being a novice framebuilder's custom frame? It would explain the crack; they may have cooked the top headlug in the process.
It's obvious there was some tension in the frame seeing as the top of the tube pulled back too. Perhaps the mitering was slightly off and the builder forced the HT into position and brazed it in under tension?
-Kurt
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