Well, decided to pull the engine and do it right.
I can't help myself.
Checked the torque of all bolts. All good.
Pulled the heads and can't blame the gaskets, they were fine.
Pressured up the oil system before head pull (no manifold) to watch it work, lotsa oil, no leaks visible or audible.
Pulled the heads and pressure checked the passages with air, no leaks.
Checked/pressurized bolt holes next to the head oil feeds, no leaks.
The block looks great. Hard to believe that it's cracked. Would've heard or seen something.
Gonna pull the heads apart and check them thoroughly.
On the positive side, the mechanicals all look great.
Plugs are perfect.
The search continues.