Looks like the head of a valve dropped and the other valve from that cylinder is wedged up into the port, from the picture of the cylinder head combustion chamber. Or something (metal, nut, bolt, spark plug, who know) went into combustion chamber. Looking at combustion chamber and piston I would guess itās the head of the valve that did that, from all the marks on the combustion chamber and piston, but why did it drop or snap of is the question? And where is the head of the valve, probably in the bottom of the oil pan?
I suspect with that kind of damage the engine was running and it came to a sudden stop and wouldnāt, turn over. If the crank and con rods are good it would be a good project for a new pistons, cylinder barrels, and complete cylinder head from Thiel ( I hope I spelled that right). Being from Europe I would send him a email with pics and ask for a quote, after tearing down the engine and checking it over
