I drained the coolant out of the block and pulled the intake manifold…
…then pulled the head. I had forgotten that this head was the one that was originally on the right side of the engine (and not the one that was more significantly damaged when the nut went through the engine). That makes me suspicious that the problem is not in the head. Given that we’ve eliminated everything in the valve train, there’s not much else that could be causing this problem.
