The 60 hp engine was designed to replace the four cylinder and was not made for long. it was replaced by the 226 six. also the v8 60 is phsically smaller and was popular in race boats and midgets. I dont recall the first fullsize flathead displacement but sometime in the thirties it reached 239 cid and it stayed that size until 53. The mercury was 255 cid achieved by using a 4" crankshaft vs 3.75 inches for the 239.