its second bodystyle came out in 1967, its third in 1969 and its fourth in 1971. bigger, more powerful engines were offered starting in 1967, making some mustangs into musclecars. some of those special mustangs had special names such as mustang gt, mach 1, boss 302, boss 351, boss 429 and 429 scj, or "super cobra jet." by 1971, the mustang had become a much larger car. the car grew in size so that ford could put its biggest engines in it, but insurance companies were charging very high prices to insure powerful cars and sales began to drop. many people missed the original, smaller mustang.