Rare 1975 Ford F-250 High Boy With Swapped 12-Valve Cummins

Automotive technician Brendan Scully has two things he openly admits. First, he likes diesels. Second, he has a soft spot for classic Ford trucks. Combine those two passions and the result is this Cummins-powered 1975 Ford F-250 High Boy 4×4. What started as a vintage Ford workhorse eventually became a diesel-fueled torque machine that blends classic truck character with the unmistakable rumble of a Cummins 12-valve. The rugged Ford showed off its oil-burning heart while parked in Diesel Alley at the 38th Annual Steve Shannon Summer 4-Wheel Jamboree in Bloomsburg, Pennsylvania.

Gas Engine Failure Was The Catalyst For This Build

Scully’s High Boy rolled off the assembly line on May 27, 1975, at Ford’s San Jose, California assembly plant, one of two facilities producing the trucks at the time. Decades later, around 2012, the truck migrated to the East Coast. Scully eventually purchased it in 2014 from a seller in Richmond, Virginia.

For a while, the truck served as his daily driver. That routine came to an end in 2015 when the original 390 cubic-inch V8 began giving him trouble. Rather than rebuild the gas engine, Scully saw an opportunity to move in a completely different direction. The solution was obvious to a diesel fan. The Ford would receive a Cummins turbodiesel.

During the transformation, the truck was taken apart extensively. The body was removed from the frame so the chassis could be sandblasted and refinished. Scully replaced every nut and bolt associated with the suspension, body, and engine. He also rewired the entire truck using a Painless Performance Products wiring harness. Interestingly, the body, paint, and interior were left largely untouched, preserving the truck’s vintage personality.

In With The Cummins Turbodiesel

At the heart of the build sits a Cummins 12-valve turbodiesel that originally came from an older Dodge truck. Scully bought the donor truck from a friend specifically to obtain the engine block.

Once the Cummins was secured, it was rebuilt with a fresh cylinder head and several upgrades from BD Diesel Performance, including a turbocharger, injectors, and a high-power injection pump. The engine also received a Hamilton Cams 188/220 Steel Camshaft and a FASS fuel system to support the added performance.

To handle the drivetrain changes, Scully installed three new crossmembers and reinforced the front section of the frame by boxing it. This modification allowed the truck to accept a later-model F-series steering box.

Exhaust gases exit through a 4-inch-diameter exhaust system, while cooling duties are handled by a custom radiator built by Wizard Cooling.

NV4500 Manual Transmission And NP205 Transfer Case

Backing the Cummins is a stout NV4500 five-speed manual transmission, replacing the truck’s original four-speed gearbox. The swap also included converting the clutch system to a hydraulic setup in place of the factory mechanical linkage.

Power continues through a rebuilt, divorced, gear-drive NP205 transfer case, a component well known for durability in heavy-duty four-wheel-drive applications.

Axles And Suspension

The front axle is a Hillbilly Wizard–built high-pinion King Pin Dana 60 equipped with Warn manual locking hubs. At the rear, the factory Dana 60 axle remains in place, although it now runs disc brakes using a Lugnut 4×4 conversion kit.

Both axles are fitted with 4.10 gears, and the rear differential retains its factory limited-slip unit.

Leaf springs support the truck at each corner. Up front, custom springs provide six inches of lift, while the rear receives four-inch lift springs combined with two-inch lift blocks. A Skyjacker shock absorber is mounted at every corner.

The suspension lift clears a set of meaty 39.5x18R16.5LT Interco Super Swamper TSL Bogger tires wrapped around 14-inch-wide Weld wheels. Steering improvements include a custom crossover steering system from Offroad Design. Additionally, the truck features ladder bars and a track bar supplied by Far From Stock.

Inside And Outside

Inside the cab, the High Boy retains much of its original personality with a few carefully chosen upgrades. An A-pillar-mounted dual gauge pod displays turbo boost and EGT readings, keeping tabs on the Cummins’ performance. The truck also features an aftermarket steering wheel and an LMC Truck head unit with Bluetooth connectivity.

Outside, the Ford wears its age proudly. Scully intentionally left the exterior largely unchanged, allowing the truck’s natural patina to tell its story. The weathered finish only adds to the appeal of this nearly 50-year-old workhorse.

The end result is a High Boy that perfectly merges vintage Ford character with the unmistakable torque and sound of a Cummins turbodiesel.