The "Adult-a-stang" has under went many transplants its currently on its 3rd engine. The Mustang started out as a "babystang" 170cc original straight six. Not long after it was purchased a 200cc 6cyl upgrade happened in 1999.. The Mustang grew up to a lumpy cam-ed 289 that was installed from a '65 falcon I purchased for $600 in 2002 as a young adult.