I have had a bent exhaust valve (obviously not sealing) and found that water was pulled into and puddled in the MPI intake plenum. Of course, I new I had a problem because the engine was missing.

How does the reversion put water in the oil ?

A few ways.

1) leak down after shut down (past rings over time).

When I found it, running the motor on a test stand, I would run it for 5mins or so and the oil was milky. I changed the oil and tried it again and same thing. I could see the water walking up the inside of the exhaust pipe, at idle.
I was told at that time, it would enter the exhaust and go right past the rings in the oil pan.. Seemed to happen very quickly.

i was told that gil headers had promble merc. made the idle at 900rpm that stop the water from coming in. i agree with these guys go dry then you don t have to worry . thats wt i am going to do had same deal going on my motor . good luck

Check your intake manifold and make sure it was sealed properly. This lets water into the oil sometimes when the bolt around the water jackets aren't tightened enough or if the intake is touching the block and not letting the gasket get squeezed properly.

I ran a 240/248 with wet GILS before and the engines are still purring like a kitten for the guy I built them for. No issues except they need bigger fuel tanks and deeper pockets.

It could be reversion though.

The good thing is that you are running them in on a test stand. Awesome call on your part.

Good luck and keep us posted.