Jerry Heasley
January 9, 2017

What kind of crazy person pulls the super-rare 429 Cobra Jet big-block out of a 1971 Mustang convertible, and installs a Boss 429? “I’m not sure because I was not that person,” Kirt Fryer says. Kirt does own the car, which was getting loads of attention at the Mid-America Ford & Shelby Nationals in Tulsa, Oklahoma. Mustang people had to know this 1971 model was a modified, especially with eight Hilborn fuel-injection stacks on top of the engine, the wild interior with exotic carbon-fiber, and 17-inch American Racing wheels. Fryer is a Tulsa area local who is well known in the Mustang world as a connoisseur of performance 1971-1973 Mustangs. That explains why he can quickly spout off production figures for Ford’s last model year of the big-block Mustang convertible. Ford built nine of them with the four-speed transmission and 23 with the automatic—for a total of 32. Perhaps this is why Fryer just couldn’t pass up this 1971 model, one of the nine four-speed cars, in a trade with another 1971-1973 guru and collector, Mickey Grafia, of Louisiana.

Both men knew the provenance. Drew Alcazar, today of Russo & Steele Collector Automobile Auctions, but formerly the owner of Concours Restorations in Rancho Cucamonga, California, had found and done a ground-up restoration of this Mustang rarity many years ago.

The paint color is Medium Blue Metallic, which is the stock color. Kirt Fryer did not have to repaint the body.
Kirt bought an extra-flat hood and cut a hole to install a Boss 429 scoop.
The last Mustang big-block convertible was the 1971 model. It’s amazing that just 32 were built.

“Drew remembered going to buy the convertible somewhere in North Dakota and driving it back to California. He told me a big, long story about it. And then he did the restoration work. It was all-matching numbers. He ended up selling it to some guy in California who spent like 100 grand having a bunch of custom work done on the car.”

The surprising modifications included replacing the original 429 CJ with a 429 stroked and bored to 540 ci and backing it with a five-speed Tremec transmission. Inside, the previous owner added carbon-fiber floor panels, a carbon-fiber dash, and more comfortable seats, which Kirt does not know the origin of.

When Kirt came across a Jon Kaase-built custom Boss 429, he got an idea. Why not drop this engine in the ’71 convertible? He had always heard the bigger engine bay of the 1971-1973 series Mustang would hold a Boss 429, but had never seen the combination. At least this installation answered the fitment question and created a what-if car with historical interest. “I had to do a little bit of work on the steering components, but the engine bolted up to the stock motor mounts, no problem,” Kirt says.

This blue top fits very well with no wrinkles.
Kirt obtained this 1971 convertible in a multi-car deal. The car had already been highly modified inside and under the hood. Had Ford put a Boss 429 in a 1971 Mustang, they might have used the signature Boss 429 hood scoop. Our guess is this car will go back to stock one day due to its extreme rarity and collector interest. But for now, Kirt says it’s a fun driver. He actually drives and enjoys his 1971 Boss 429, which nobody else can say.
The interior is “quite modified,” according to Kirt. Carbon-fiber is spread liberally throughout the cab—dash, console, and floorpans. The steering wheel is a Grant 3-spoke.

Jon Kaase Racing Engines of Winder, Georgia, built the Boss 429 engine that Kirt had come across in his car dealings. Jon’s build started with an aftermarket aluminum Boss 429 block sourced from CNC Motorsports. Jon installed their own aluminum head that is a replica of Ford’s head, but with a conventional head gasket, instead of the exotic O-rings. Jon’s Boss 429 also has modern serpentine belts and the Hilborn fuel-injection system. The unknown person in California who did the modifications chose the Tremec five-speed that spins a set of 3.50:1 gears in the original N-cased 9-inch rear end with Traction-Lok. “The car is really fun to drive. It’s got lots of power,” Kirt says.

Kirt could not give us any quarter-mile times. He doesn’t put this classic on the drag strip. It’s purely for cruise and show. We have to think that one day either Kirt or a future owner will put this car back to stock. A big question is what happened to the original, matching-numbers 429 Cobra Jet? After all, a 1971 429 Cobra Jet Mustang convertible is worth some serious bucks. Apparently, the engine is lost. If anybody out there has a clue where the engine is located, contact me at my “Rare Finds” email, and we’ll do a special report on finding it.

The back seat appears stock.
Carbon-fiber inserts accent original door panels.
American Racing wheels are 17 inches in diameter. The suspension is factory stock, except for the larger wheels and tires.
Ford’s Vehicle Certification Label on the driver’s door reveals the “J” code for the 429 Cobra Jet.
The Boss 429 is still an option for car builders today, thanks to Jon Kaase Racing Engines, who built this Boss 429 to run on pump gas. It delivers 800hp “all day long,” according to Kirt. The serpentine belt system is part of the modern build. The Hilborn injection system is electronic.
The 1971-73 Mustang community has bequeathed guru status upon Kirt Fryer. How do we know? He’s just owned so many of these cars and knows so much about them.
The car won the modified class at the Mid-America Ford & Shelby Nationals in June 2016. Other than the hood scoop, though, the body is not modified. Ford offered the big-block in the Mustang for the last time in the 1971 model year.

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