Gasoline will not cause two valves to drop and trash out a piston and the cylinder head. Excess Gasoline would trash out the fuel system the engine would just stop running and not drop the valves.
Look for: 1) Thinned oil that caused the hydraulic lash adjusters to fail and make the valves hammer until the heads fell off. Cam may be trashed too. 2) Clogged up intake from goo caused by excess EGR and oil vapor. 3) Check the turbo shaft for excess wobble, another item caused to fail by thinned out oil. 4) Check oil passages for being clogged up with soot sludge that kept oil from getting to the head causing the same as 1 above. 5) Check VRT vanes to see if they are stuck and could cause over heating from over boost, rare but it can happen.

Did this CRD come from an area with lots of steep mountains? The owner could have used the cruse control for towing up the steep grades and trashed the engine by driving up the EGT through the roof.

The turbo looked and felt fine, very minimal if any shaft play if I remember correctly. I honestly don't know where the jeep came from, my boss bought it from auction as is pretty much so we know just about as much as you do. It was only this one cylinder that was affected, the other three were perfectly fine so were are going to just rebuild the block.

@geordi - It's always sad to see something go in any way, shape, or form. I sent you a PM btw asking you about your heads.