Putting it out here for comments
Valve stem seals Is a known problem especially after a long standstill
Piston tops looks More or less OK
Cylinder head sooty , black
??? Proposition -- Valve stem seals not there or cracked --Letting oil flow down smoking consuming oil and eventually hit the Valve seat loosing compression.
So the spark plugs in -- turn it over and pour in Gasoline will flow right through and the Cracked valve stem can be seen or after dismantling