The Boss 429 Mustang is a high performance Ford Mustang variant that was offered by Ford in 1969 and 1970. It's worth noting that famed engine builder Jon Kasse currently reproduces the iconic cylinder heads that make up the "boss 9" engine architecture.
The Boss 429 is recognized as being among some of the rarest and highly valued muscle cars to date. In total there were 1359 original Boss 429s made. The origin of the Boss 429 was to fulfil Ford's need to homologate the 429 semi-hemispherical engine for NASCAR racing. Ford was seeking to develop an engine that would better compete with the 426 Hemi from Chrysler in NASCAR's Grand National Division, now known as the NASCAR Cup Series. NASCAR's homologation
rules required that at least 500 cars be fitted with this motor and
sold to the general public. After much consideration, it was decided by
Ford that the Mustang would be the car that would house this new engine.