The first Ford Mustang V8 option had a displacement of 260 cubic inches. It was available when the Mustang debuted in 1964, in the period enthusiasts commonly call the 1964½ model year.
The 260-cubic-inch small-block V8 gave the new Mustang a substantial performance step over its standard 170-cubic-inch inline-six. Early V8 cars wore “260” badges over a wide V on their front fenders, making the engine size part of the car’s visual identity.
The 260 did not remain the Mustang’s main V8 for long. For the regular 1965 model year, Ford shifted the lineup toward several versions of the 289-cubic-inch V8, including two-barrel, four-barrel, and high-performance configurations. That later 289 became much more famous, which is why it is often incorrectly remembered as the first Mustang V8.