Bitter taste of defeat! So much coolant in the oil pan.

Trevor B said
Am I missing something obvious?

Don't know. I'm with Rob. All we can do, sitting here with our imaginations, is guess.

How reliable is the source from which you got those heads? Even so, one of them could have a problem.

As others have said, "the odds" are that there's a problem, somewhere, in the timing cover / water pump / etc.