So far, fairly certain it isn't the manifold.

Now looking very hard at the aftercooler. I replaced the aftercooler 6 or 7
years ago. Would not have suspected this relatively new part. I can't figure
out how enough water could get into the cylinder through the aftercooler,
(which is mounted below the intake manifold) to hydrolock the engine.
One would think that the failure of a tube or two in the aftercooler would
introduce
*some* water, or vapor, into the cylinder but not a huge puddle or enough to
create a hydrolock.

Will keep developments posted- somebody else may learn from my misfortune.