The wild success of the original Ford Mustang left even Blue Oval executives surprised, and it wasn’t long before executives at the Mercury division were clamoring for a muscle car of their own. What they got was the Mercury Cougar in 1967, an upscale Mustang available only with the Mustang’s V8 engine options. This included an attempt by Mercury to market a pair of Boss 429 powered Cougars to drag racers, an attempt that fell flat.

This pair of special cats disappeared from the world until the past decade, when both Boss 429 Cougars resurfaced. One of those 429 Cougars, the one driven by “Dyno Don” Nicholson, has been fully restored and will roll out at the 2014 Ford Nationals at Carlisle alongside other historic Fords and Mercurys, reports Hemmings Auto Blog.

Rated at 375 horsepower and 425 ft-lbs of torque, on paper the Boss 429 Cougars seemed unstoppable. However, these unofficial Ford project cars weren’t assigned special VINs, and their performance proved disappointing. This led Dyno Don to replace the Boss 429 with a 427 Cammer engine, while “Fast Eddie” Schartman used his Cougar to teach tuning and racing clinics.

The cars fell off the radar for awhile and into a state of dismal disrepair requiring a lot of time and money to restore. The Schartman car is still a work on progress, but Dyno Don’s old ride is ready to wow the crowds at Carlisle this year, though owner Ed Meyer hasn’t decided whether to install a Boss 429 or Cammer 427 into his restored ride. We say for authenticity sake though, he go with the Boss motor as a nod to what might-have-been.