Rick,

 

Looks to me like the engine ingested something that didn't agree with it. Probably aluminum from the lack of brinelling on the valves (the speckels on the valves are just surface smears and cleaning aren't they? Tough to be sure from the photos).

 

It has a very similar appearance to an episode of light detonation I had that liberated a section of the head land from the piston. The piston frag rattle around until it closed the plug gap and then either disintigrated or managed to get out throught the exhaust valve. I felt an initial engine shake and then just a miss with a loss of power.

 

Rob