I’ve been fortunate to cross paths with many passionate Mustang owners over the years—especially through my involvement with Mustang Week in Myrtle Beach. But every once in a while, someone comes along with not just a car, but a legacy on wheels. That someone is Bobby Siebenmark—known to many around North Myrtle Beach simply as “Bobby Mustang.”
I didn’t meet Bobby in the early years of Mustang Week—it was later on, as the event had really hit its stride. But even then, his enthusiasm was electric, and the bond he had with his car was unlike anything I’d seen. Now retired in North Myrtle Beach for the past 10 years (originally from Ridge, MD), Bobby spends his time enjoying life by the ocean—and tearing up the road in his stunning 1969 Mach 1 Mustang.
Nicknamed Misty—short for Mistress—this Winter Blue beauty has 160,000 original miles under her belt, with 35,000 of those laid down after a full restoration 13 years ago. “I’ve owned her for 13 years,” Bobby told me. “She came from a local friend back in St. Mary’s County, Maryland—Callaway, to be exact. But what sold me was the color. That Winter Blue blew me away the moment I saw it.”
But Misty is far more than a pretty face. Beneath the hood now beats the heart of a 408ci Stroker from Blueprint Motors, pushing out 500 HP—a big step up from the original, worn-out numbers-matching 351W. She’s backed by a built AOD transmission with a Lentech valvebody for manual shifting and overdrive on demand, paired to a 9-inch 3.90 Detroit Locker rear. Add in Unisteer rack-and-pinion, Total Control Products dual-adjustable coilovers, tubular control arms, and a 1” Shelby Drop, and you’ve got a street beast with show-winning looks and strip-ready power.
“The best upgrade by far was the AOD with the manual shift valvebody,” Bobby said. “With that 3.90 rear gear, it woke the car up! And the best part? I can cruise at 80 MPH on Ocean Highway in overdrive without even pushing the tach.”
Most of the work on Misty has been done by Bobby himself, with some heavy lifting handled by a loyal crew of friends. “Chris Reissman and Bradley Cooper at Coastal Speed did great work on the shock tower replacement. To Steve Pisarski, thanks for the engine pulls, you are truly a great friend. I’ve got a strong network and a supportive wife—Debbie Siebenmark—who not only loves the car but also keeps everyone happy with her baking. (Check her out at @cookiesbydebbie.)”
The Mustang has made its rounds—showcased from Myrtle Beach to Charlotte Motor Speedway—but a few honors stand out. “Winning Best in Show Club Choice with the Southern Maryland Mustang Club 12 years ago was special. Amy Rebecca was president, and Tom Billings was vice president then. And getting Best in Show for 1969–1973 Mach 1 at Mustang Week 2018—that was unforgettable.”
Despite the show accolades, Bobby’s not afraid to let Misty stretch her legs. “Ocean Blvd sees her at least twice a week. She’s not a garage queen—she’s a driver. And yeah, I’ve smoked my fair share of Chevys at stoplights,” he laughs.
He’s even got his sights set on road course fun. “All that’s left is rear TCP suspension. Once that’s in, Misty’s going road racing.”
The 1969 Mach 1 is becoming increasingly rare and expensive to restore. “If you don’t have the skills, the space, and the right tools, you’re going to drop six figures trying to build a car like this today,” Bobby says. “I feel blessed every time I drive her.”
That gratitude extends to the community Bobby’s built around Misty. Whether it’s the Southeastern Stangs, the Blue Mustang Registry, or the many enthusiasts and clubs he’s supported and hosted, Bobby has become a central figure in the regional Mustang scene. Last year, he played a key role in the host club for Mustang Week 2024—something he calls one of his proudest moments.
“Being part of this world has changed my life,” Bobby reflects. “The friends I’ve made, the stories I’ve heard—this car has been a blessing. Even Chevy guys respect her.”
So next time you’re cruising through North Myrtle Beach, keep an eye out for that Winter Blue flash and the polished Billet Specialties Drag Lites glinting in the sun. That’s Misty. That’s Bobby Siebenmark. And that’s the spirit of Mustang Nation—alive and well.
