The third redesign of the Mustang appeared for the 1969 model year and the car grew in size once again. Also, they changed the engine choices as well as the equipment list. Another thing Ford did was concentrate the Mustang lineup in two main directions. One was luxury with the new Grande notchback model and other was pure muscle with three new models, the Mach I, Boss 429 and Boss 302.
In addition, Ford introduced the legendary 428 Cobra Jet engine as a regular production option, which put the Mustang among the fastest muscle cars of the era. The best-known muscle Mustangs from 1970 are the Mach I and Boss tandem, with the 302 and 429. The Mach I was an affordable performance model with the 428 CJ as a top engine option.
The Boss 302 was a pure road racing car with the high revving 5.0-liter engine. The mighty Boss 429 was a car Ford designed to carry a special semi-Hemi big block engine destined for NASCAR racing. The Mach I was the most popular while they only produced the Boss models in limited numbers, discontinuing them for 1971.