In some cases, real Boss 429s may have indeed gone to the junkyard. Check out the story of Keith Clark's Boss 9. He tells us, "In 1975, my future brother-in-law needed a car to drive to work." Being a car guy, Clark checked out the local junkyard and found this 1970 Boss 429 with no engine under the hood—the original Boss 429 engine had been stolen and was long gone.

For two grand, the yard sold him the 1970 Boss 429 and threw in a running 429 CJ. That price might sound pretty sweet from a 2016 viewpoint, but nickels were the size of wagon wheels in the mid-1970s: A hamburger was 50 cents and a gallon of gas was 59.9 cents.

"My brother-in-law had just gotten his first job in construction, and was making decent money for the day." Flared fenders and all, this Boss served as a work car for two years—enough time to round up a real Boss 429 engine. "He took the [Boss 429] engine apart as far as you possibly can. The only way you could put that engine in more parts was to use a hammer."

See all 4 photos

In 1977, his brother-in-law decided to get married and sell the Boss 429. Clark was very interested, no matter the modifications. The car still had those wild fender flares and a Shelby rollbar, and because it was during the CB radio days of the 1970s, somebody had drilled holes in the dash and a CB antenna sprouted from the right rear quarter panel. Half of a hinge on the rear roofline to mount window slats had broken off and dented the body. Nevertheless, this 1970 SportsRoof was a real Boss 429, KK2388. Thirty-nine years ago, in 1977, four or five grand including the Boss 429 engine was actually not that cheap.

A full restoration was out of Clark's budget. In his garage at home, he wet-sanded the body and applied a lacquer paint job, keeping the same Grabber Orange color. Then, after assembling the Boss 429 engine, he just drove the Mustang like a regular car. The body had some rust "underneath and in places I don't want to talk about," Clark said. "I can drive the car because it's not perfect. If it was a perfect car, I'd feel bad about driving it."

See all 4 photos

Looking back, the Boss was seven years old when Clark got it. As the years passed, his attitude changed as the car aged and became more valuable. "I used to feel bad about the flares until I went to the 100 years of Ford show. My nephew and I went for a walk, and on the way back he said, 'Whoa, wait a minute? How many people are standing around all those Boss 429s that are nice and perfect?'"

Keith looked and saw about five people looking at the half-dozen restored Boss 429s, but he saw 30 to 40 people standing around his Boss. He said, "Not everybody is a fan or knows or cares about Boss 429s, the collectability. Lots of people just like the car for what it is."

According to Clark, "It's a Hot Wheels type, flared out, radical, hot rod." That's why he installed a Hot Wheels sticker on the rear. During his 39 years of ownership, Clark has turned down many offers that he says are, "Rarely over $100,000." Instead, he prefers to keep his 1970 Boss 429 for driving and showing.

"It is the only Boss 9 that is daily driven that pulls a dune buggy that has a trailer hitch, that has flares, and that you can see back into the past how it was modified. I like that."