The 1966 Mustang Fastback occupies a rare space in car culture. It is old enough to be iconic, yet it still feels instantly usable, intuitive and right-sized in a way that connects across generations.

When Ford introduced the 2+2 fastback part way through the 1965 model year, it gave the Mustang something the coupe and convertible couldn’t offer: a profile that looked like it belonged on a ...