A vast majority of the stock Model A heads will have a small raised casting mark on the top of the head in front of the water outlet above the boss for the water pump. The Snyder's head is smooth in that location. The first picture is a stock Ford head, the second is a Snyder's 5.5 head. This is not a foolproof way to identify a Snyder's head since I have seen other, older, aftermarket heads with no identifying features or casting marks. Gar Williams