Something doesn’t look right in your first photo as there is no compression relief at all on that cylinder head. The only thing I see is the hole on the rewind starter for the pivot pin for the valve linkage. Either the head has been changed over or the whole powerhead has been replaced at one time.
Look on the block for a welch plug with some numbers stamped on it. It’s about the size of a quarter and might be on the top of the block. The numbers should match the ID plates numbers which is mounted either on the front or the sides of the transom clamps.
