I appreciate the info Frank.Sort of correct. The early 12 was similar to the Evinrude 14hp. It is often called the wedge head block. Later 12hp design was similar to the Evinrude & Johnson 15hp. There is a world of difference between the "early" and "later" models. This guy's 1957 motor is the "later" one with removeable cyl head, based on the 15hp, but with smaller bore.