HOLY SHEET!!!! H/C car with problem
Put it in some boiling water and it never openned? or just guessed?
If this overheating & coolant leaking happened so soon after a head install I'd have to say the gasket just didn't seal.
New headbolts were used right?
+1 advantages for not running a thermostat.
It doesn't happen often but this goes to show it can be bad when it does.
Yeah obviously the mating surface/s have warped now from the overheat, so they need to be straightened.
You probably did nothing wrong on the assemble... it's just bad luck about the tstat.

