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All Hail the Duke: A Cummins-Powered K50 Built for a King

Randall Robertson has his best ideas between 2 and 2:30 a.m. A vision comes to his mind, waking him up to jot down some notes, and within 20 minutes, the complete design for his next build is laid out on paper. This unconventional, yet effective, process was the spark that set off the fire in Randall to build his latest instant-classic Chevy truck, “The Duke.”

The Duke

Randall owns and operates Rtech Fabrications, a custom truck shop based in Hayden, Idaho, that specializes in ’62–’72 Chevy trucks. Rtech is no stranger to unique, larger-than-life builds. Past models the company has built, such as the “Cowboy” and “Drill Sergeant,” are proven showstoppers that have captured the hearts of Chevy truck fans of all ages. But Randall never builds the same truck twice: “If it’s already been done, I’m not going to build it.” That premise brought on the idea of building The Duke, a truck that Randall challenged himself with. “The Duke is a refinement of everything I’ve built so far,” Randall explains.

chevy k50 cummins rtech fab 2639

Classic Chevy trucks are some of the most popular restoration projects among enthusiasts, mostly due to a wide availability of aftermarket parts, detailed restoration guides and a wealth of knowledge in building them. So what makes the Duke stand out among the hordes of other classic GM trucks displayed at car shows across the nation? For starters, the Duke is much, much larger than your standard regular-cab, shortbed restomod. Randall and his team at Rtech are masters of building custom trucks in configurations that Chevrolet never produced. The Duke is based on the medium-duty C50 chassis, extended to four doors with an 8-foot tilt bed. But, technically, The Duke should be called a K50, which is GM’s designation for a 50 series four-wheel-drive truck. But just like most of Rtech’s builds, the devil is really in the details. Simply slapping a crew-cab body together and extending a chassis isn’t much of a build. Randall wanted to build this truck to look and feel like a classic Chevy, but perform like a modern diesel powerhouse.

The Duke side view

Randall’s carefully thought-out design is what makes The Duke a real showstopper. The drivetrain had to be powerful, strong and easily serviced. Under the hood sits a 5.9L Cummins 12-valve diesel engine, tuned to a reliable 450 hp. Behind it sits an equally impressive NV4500 five-speed manual transmission, built to deliver massive power with reliability and ease. Rtech used an NP205 transfer case to deliver power to the front axle, which happens to be a GM Dana 60. The rear axle is a GM Corporate 14-bolt, built to handle heavy loads and big tires. The brakes on The Duke are custom made and are now available through Rtech Fabrications. They use a drilled and slotted design, with a heavy-duty RV brake pad to increase braking performance. After all, stopping a truck this big isn’t easy.

The 12 valve Cummins under the Duke's hood

In Randall’s opinion, simplicity is key as long as it does the job. He didn’t want to overcomplicate this build with high-tech suspension systems, so the front and rear is lifted on leaf springs, much like you would find on a truck of this age. Rtech installed a set of Bilstein shocks to beef up the ride, but painted them black to give the appearance of a factory underbody. A set of load-leveling airbags help do the heavy lifting when The Duke is towing.

The Duke's suspension

From the outside, The Duke looks like a well-kept, clean, old truck. But that was no accident; Randall designed it to resemble a factory truck, with some key upgraded features. The front and rear bumpers began as a pile of sheetmetal, and Randall worked them until he was happy with what he saw. The final result is a classic style with ample protection. The running boards are made from ¼-inch cold-rolled steel tubing as well, making The Duke strong enough to withstand a hit from any side.

chevy k50 cummins rtech fab 2503

One unique feature on The Duke that you wouldn’t know about by just looking at it is the tilt bed. Originally used to make dumping materials out of the bed easier on the jobsite, the tilt bed serves a much more mellow function these days. Under the bed of The Duke lies a utility box housing the central heat and A/C systems, batteries, the 60-gallon fuel cell and the bed’s hydraulic lift. When the bed is down, this utility box is virtually invisible. The tilt feature allows for easy access to these systems, and let’s be honest, it looks way cool.

The tilt bed on The Duke

Moving inside The Duke, a few things catch the eye. Randall decided that masking new components with a classic skin is the best way to achieve a comfortable ride while staying true to the truck’s era. The dashboard is a custom-built piece that Rtech is now installing in most of its customers’ trucks. It features all the standard original equipment, with the addition of a double-din radio. “It is meant to look exactly how it would have looked if we had double-din radios in 1972,” Randall says.

The Duke's interior

Randall used the seats from a ’10 GMC Sierra for the front and rear, removed the headrests and changed the covers to a highlander-style stitching to match the original seats. The door panels were made to resemble the originals as well—with a modern twist. The Duke has four power windows, cleverly controlled by a switch disguised as a hand crank. The other unconventional feature of the Duke’s interior is the power sunroof. Randall had to completely rework the headliner around it, which came out of a ’97 Volvo 850 wagon. A leather-wrapped custom steering wheel ties it all together, giving the truck an old-school feel while driving.

The Dashboard on the Duke

It’s hard to imagine there’s an even deeper level of detail to The Duke, but Randall didn’t just stop at restomod. Some of the unique features making Randall’s trucks so highly sought after are Rtech’s techniques for delivering a ride that’s smoother and quieter than even the latest model production trucks on the market. For instance, the 12-valve Cummins—although legendary for its power and reliability—is not a quiet or calm diesel engine by any stretch. Randall used hydraulic motor mounts from Mercedes-Benz to bolt the engine to the chassis, as they do the best job of reducing the rattle and noise from the Cummins.

The headliner in The Duke

Another unseen detail is the firewall. Randall custom-built the firewall with sound-deadening material and angular pieces to divert sound away from the interior. The rear of the cab is coated with rust-inhibiting paint, rubber-coated, layered with normal paint, then topped with sound-deadening material, followed by carpet and padding. In fact, The Duke’s interior so quiet that Randall later added a tachometer to the instrument panel because he couldn’t hear what rpm the motor was running at when shifting the transmission. That’s unheard of for a Cummins 12-valve.

The Duke's rear bench seat

If you couldn’t tell yet, Randall likes his peace and quiet, even while driving a 5-ton diesel truck down the highway. So what tires does a man like Randall put on a project like this? Some 40x15.50R20 Nitto Trail Grapplers were his weapons of choice for The Duke, and Randall had a good reason why. “The Trail Grapplers have been epic. They are incredibly quiet and round down the road, and they don’t feel like driving a big truck with big tires.” Randall also mentioned that from The Duke forward, all his builds and customers’ trucks will be built standard with Nitto tires on them. The KMC XD829 Hoss 2 wheels bring a touch of modern to The Duke’s looks as well.

40x15.50R20 Nitto Trail Grapplers

While The Duke may be the ultimate classic Chevy tow truck/daily driver, Randall has a few more builds in the works. Rtech Fabrications will be working on two new trucks, nicknamed the “Dino” and the “Ponderosa,” in addition to a K20 limo project. But for now, The Duke is out of show season, and Randall will enjoy driving it to and from the shop for a while. That is, until his next 2 a.m. idea comes to life.

Photographs by Tim Sutton

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