Fit For The Farm

A Show-Stopping, Cummins Cab-Over Conversion—Built For Work And Play

Greg Noble has a classic car, John Deere tractor, and motorcycle collection that would be the envy of any collector that accumulates either of those things, so why build a cab-over GMC with a 12-valve Cummins in it? Turns out, when you own multiple farms, bear an affinity for old GM’s, and have a bunch of wild ideas running through your head, you can easily justify the need for a one-of-a-kind vehicle. And after enlisting the help of friend Cale Kern, one of the premiere hot-rod builders in the Midwest, there was no stopping the Orleans, Indiana resident’s plans to build a one-of-one ’47 GMC COE.

Kansas Gem

To say that Greg was fired up to get the project underway was an understatement. He even secured four different COE makes from the same era to choose from. And although it was determined that a Duramax would fit in the ’53 Chevy he’d hauled home, the inline architecture of the 5.9L proved a better fit for his ’47 GMC, a clean find from Kansas. Its original frame was in great shape and the patina’d body was perfect for a guy who’s big on original paint. So with the truck decided on, it was time to find an engine.

Scheid 12-Valve

Believe it or not, Greg Noble’s original plan was to repower a cab-over with a Duramax. But after consulting with friend Cale Kern of Cale Kern Hot Rods, who would be spearheading the project, the decision to go with a Cummins—a much more packageable engine given the lack of real estate under the hood—was made. Even then, fitment of the inline-six proved very tight, and called for long hours. Throughout the process, Andy Thomas from nearby Southern Indiana Diesel Service lent a helping hand, even sourcing the engine, transmission, and clutch that would make up the powertrain.

After dropping a core 12-valve block off at Scheid Diesel, the folks there pieced together a long-block more than capable of handling a little abuse. The 5.9L benefits from ARP main and head studs, ARP bolts in the factory rods, Mahle cast-aluminum pistons and bearings, a Scheid street cam, and a fire-ringed head equipped with 60-lb valve springs. Other aftermarket parts included a billet-aluminum front cover, tappet cover, and intake plate, along with a Fluidampr. A Fleece coolant bypass system keeps cylinder temps in check across the board.

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Engine And Turbo Fitment

Leaving nothing to chance, Scheid Diesel got the nod for supplying Greg an overbuilt yet potent P-pumped 5.9L 12-valve Cummins. Beyond the ARP head stud visible here, the B-series is fitted with ARP main studs and rod bolts, Mahle cast-aluminum pistons, a Scheid street cam, and a fire-ringed head with 60-lb valve springs. On the fuel side, the 12mm P7100 has been massaged to flow as much as 400cc’s worth of fuel and support as much as 4,500 rpm. It feeds a set of 5×0.013 injectors by way of custom bent, .093 stainless steel lines. As for the turbo, a 62mm S300 hangs from a third-gen, motorhome-style T4 Steed Speed exhaust manifold.

In the words of Andy Thomas, owner of Southern Indiana Diesel Service who contributed many hours to the build, “the engine compartment is ten times tighter than it looks.” Among many things, careful consideration had to be given to turbo location, intercooler piping, and the injection lines. The .093 stainless lines had to be custom bent by Scheid in order to clear the floorboard of the cab, even spanning between the BD individual valve covers. For its low and rearward mounting position, a third-gen, motorhome-style Steed Speed exhaust manifold was chosen for mounting the turbo, an S362 with a T4 turbine inlet flange.

NV4500 Integration

Sure the narrowed 14-bolt, Ridetech HD four-link system, and Firestone air bags look and function perfectly now, but in the early-going the entirety of the rear-end had the folks at Cale Kern Hot Rods scratching their heads. All told, Kern C-notched the rear frame rails so they could be brought in roughly 6-inches. The narrowed 14-bolt axle is fitted with a 4.10 ring and pinion, a limited slip differential, and Moser axleshafts.

Arguably, there is not better old-school diesel combination than a 12-valve Cummins matched with an NV4500. The decision to go with a manual transmission was fitting for a truck that would see use around the farm, but its integration—particularly in the cab—wasn’t as straightforward as you might think. First, the shifter wouldn’t clear the back of the cab. And then the original parking brake lever couldn’t be retained due to contacting the passenger seat. These problems were solved by turning the shifter around and by switching to an E-Stopp (electric) parking brake. Southern Indiana Diesel Service furnished the rebuilt gearbox, which is graced with a larger, 1-3/8-inch diameter input shaft and a quiet street dual disc clutch from Valair.

Air Ride

When not just any NV4500 transmission will do, you source one, have it completely rebuilt, and throw in a larger, 1-3/8-inch diameter input shaft for good measure. The five-speed manual also benefits from a short-throw shifter and sports a quiet street dual disc clutch from Valair. And because the original parking brake couldn’t be retained due to its lever location in the cab, an E-Stopp electric parking brake was added.

Due to obvious space constraints with the cab-over design, the intercooler couldn’t be mounted in front of the Cummins. By opening up the front bumper (and also making it taller), Cale Kerns was able to locate the 28-inch long, 4-inch thick core unit directly behind the bumper. The 2.5-inch cold-side and hot-side piping has since been upsized to 3-inch.

Full air ride offers both a stable feel when loaded and comfort when cruising. It’s made possible in the rear thanks to an HD four-link system from Ridetech, which incorporates air springs rearward of the narrowed axle. Custom-fabricated lower control arms provide the mounting point for the Firestone bags up front, and the rack and pinion out of a Dodge Sprinter helped modernize the truck’s steering. A bit of resourceful engineering on the part of Cale Kern Hot Rods makes it possible for the truck to still be driven in the event of air spring (or an air spring system) failure.

Top-Tier Craftsmanship

For optimum ride quality, Ridetech’s HD four-link system accommodates the rear air-ride while also improving handling and quelling axle wrap. The links are made from 1.5-inch diameter, .188-inch wall DOM tubing, utilize poly bushings, and use ¼-inch thick, plate-steel brackets.

Nestled inside the driver side frame rail, you’ll find a 140-gph titanium signature series fuel system from FASS. The low-decibel lift pump sends 45-psi worth of supply pressure to the P-pump up on the engine. It pulls fuel from an aluminum tank fabricated at Cale Kern Hot Rods that’s mounted on the other side of the frame rail.

Up front, C30 spindles are utilized and Kern built the lower control arms to incorporate the truck’s other pair of Firestone air springs. To minimize steering effort, a late-model rack and pinion out of a Dodge Sprinter made the cut as well. Ridetech shock absorbers are employed front and rear. Notice the hot-side piping present here, which routes boosted air to the bumper-mounted intercooler.

Other than the black, milled-down, 22×8.25-inch Alcoas proving a perfect fit for the truck, aesthetically, the real automotive creativity lies in the bed. Starting with a sketch Cale Kern put together, the 7-foot-wide piece mixes the look and functionality of a flatbed with a wrecker bed. The bead-rolled bedsides were seamlessly matched with the patina on the cab courtesy of patina master, Jerome Borris, which to the layperson makes the bed appear original. The bed is also furnished with a gooseneck ball, a cargo box at the back of the cab, and an aluminum fuel tank on the driver side that is matched with a storage box on the passenger side which contains the batteries and onboard air compressor.

Hometown Pride

The gauge cluster, built specifically to match the truck, came from Dakota Digital. Another highly welcomed creature comfort in the cab comes in the form of a Vintage Air A/C system. Thanks to these pieces, driving and riding in the COE is as pleasurable as it looks—especially on long hauls with two John Deere tractors in tow.

In the cab, the first thing to point out is that the driver seat is original to the truck while the passenger seat isn’t. But thanks to the handiwork of interior expert, Brian Barlow, you’d never know the difference. Barlow worked his magic on the seats, dash, and carpet, giving the cabin an authentic look. For comfort, both seats feature air-ride. In this photo you get an idea as to how far back the shifter for the NV4500 is positioned in the cab.

The truck’s bed has quite a story behind it. Originally sketched out by Cale Kern and coined a “marriage between a flatbed and a wrecker bed” by Greg, it’s made of 14-gauge steel but the deck was constructed from 1/8-inch thick plate. The exterior of the bed sides are bead-rolled and almost decorative, the tailgate is fully functional, and although the bed looks just as patina’d as the truck’s cab, it isn’t rusted at all. That trick was pulled off in jaw-dropping fashion courtesy of Jerome Borris. In fact, Borris matched the bed’s paint to the cab so well that a rough, rust-like texture can be felt with a swipe of the hand.

For a set of wheels that looked the part, Greg bought six brand-new Dura-Black Alcoa semi wheels and custom adapters from Dually King Industries. The 22.5’s were milled down to 22-inches and fitted with Nitto rubber. Up front, the truck wears a pair of 33-inch diameter 285/50R22 Dura Grapplers. Out back, four 33×12.50R22 Terra Grappler G2 all-terrains offer the COE plenty of load-carrying stability.

Even with COE’s making a comeback in recent years, Greg’s GMC stands apart from the crowd. Whether it’s the original paint, the semi wheels, the era-appropriate yet custom bed, or the distinctive clatter coming from the engine compartment, his cab-over creation commands the undivided attention of everyone within sight or earshot. And while the no-expense-spared nature of the build makes it what it is, so does its retention of the 75-year-old cab and frame. Better yet, throughout the course of the build Greg kept it all in the family, so to speak. Cale Kern Hot Rods, Southern Indiana Diesel Service, Ridetech, Dually Kings, and Scheid Diesel all make their home in Indiana just as Greg does—and each played an indispensable role in the project. We think it’s safe to say that Greg’s ’47 GMC—with its skillful blend of old and new—fits right in with his classic car collection.