Nicknamed the Shotgun, the Boss 429 engine was so big that Ford contracted its performance engineering vendor, Kar-Kraft, to modify the Mustang’s shock towers, move the battery to the trunk, and make the big-block fit. Only 859 were built in 1969 and 501 the following year. They’re homologation specials, built to legalize the 429 “semi-hemi,” with its aluminum heads and crescent-shaped combustion chambers, for NASCAR.
Priced at $1208.35, the Shotgun option was enormously expensive, and its huge ports and valves were better for the track than the street. But these were the most powerful Mustangs of the era, with 375 horsepower and 450 lb-ft of torque. All were fastbacks with four-speeds, 15-by-7-inch Magnum 500s, and F60 Goodyears.
[Editor’s Note: This story originally appeared as part of the 25 Greatest Mustangs cover story in the July/August issue of Hagerty Drivers Club magazine. You can find the other entries here.]