 Once I had the cover, I went to put it all back together, and before putting the belt on, I checked the crank pulley against the new cover, and they didn't match. With the crank pulley lined up on the mark I had made, it was way off from the mark on the cover, almost certainly a full tooth. Had I marked the pulley wrong, Billy asks? With no mark on the sprocket, I couldn't be sure. Was the cover from a later engine that had the timing marks in a different position? Terrifying prospect, but possible, Billy. It really is.