Story goes that the fella picked it up from the airport and made it a few miles, decided to shut it down after hearing the 'knock'. It was towed in, and the engine had seized. There is still no proper diag as to what exactly happened, but there is a new engine in the truck now. The damaged engine will be sent in to Ford for dissection and a good look-over.
Best guess is that a valve spring or guide failed.
Best guess is that a valve spring or guide failed.