Some major changes to the Mustang occurred at the start of 1965 model year production, a mere five months after its introduction. First was an almost complete change to the engine lineup. The 170 in (2.8 L) I6 engine made way for a new 200 in (3.3 L) version which had 120 hp. Production of the 260 in (4.2 L) engine ended with the close of the 1964 model year. With a new, two-barrel carbureted 200 hp 289 in (4.7 L) engine taking its place as the base V8, people started to get excited. A 225 hp four-barrel 289 in (4.7 L) was next in line, followed by the unchanged 289. The DC generator was replaced by a new AC alternator on all Fords and the now-famous Mustang GT was introduced. Available was a four-barrel engine with any body style. Additionally, reverse lights were added to the car in 1965. Originally, the Mustang was available as either a hardtop or convertible. During the car's early design phases, however, a fastback model was strongly considered. The Mustang 2+2 fastback made its inaugural debut with its swept-back rear glass and distinctive ventilation louvers.