I am interested to see what you find when you pull the head

 

The photo of the spark plug is great = beyond my experience.

 

Those spark plugs look like your engine was suffering from pre-ignition; a very rare but highly damaging condition which typically puts the engine beyond repair within a second or two. If I'm correct then the engine has most likely suffered one of the following failures (ordered from highly-likely to less-likely):

• One or more pistons with holes in them
• One or more valves bent or burned away
• One or more bent connecting rods
• Damage to the valve lifters
• Broken or damaged cam shaft(s)

I agree with Hamster108, I want to see what is revealed when you pull the head.

The above said, were I in your shoes (and time was tight) I wouldn't bother with the head; I'd find a used or rebuilt motor and swap the engine. Long story short, your engine is (most likely) toast.