Diesel Fans, Meet the Ultimate Sleeper: 6BT 12 Valve Cummins-Powered '77 Ford F-250

When you see a ‘77 Ford F-250 rolling up to a car show, you might expect to hear the familiar rumble of a gas V8 under the hood. But this particular High Boy from High Octane Classics has a surprise that’ll make diesel heads do a double take - it’s packing a 12-valve Cummins turbo diesel where Ford’s original powerplant used to live.

Steve Magnante walks us through this fascinating build that perfectly captures what happens when you take the best of both worlds and smash them together. The heart transplant comes courtesy of a Dodge Ram 2500 or 3500 that donated its legendary 12-valve Cummins to the cause. We’re talking about roughly 500 HP and 800 lb-ft of torque channeled through a fully rebuilt 47RE transmission with billet components - enough grunt to make this classic Ford scoot down the highway with authority.

The swap wasn’t just a quick engine drop either. The attention to detail shows everywhere you look, from the twin 12V batteries needed to fire up that diesel beast to the custom exhaust system that lets everyone know this isn’t your average ‘77 F-250.

What really makes this build special is how they kept the truck’s original character while adding modern capability. The Dana 45 front axle with manual hubs can handle the Cummins torque without breaking a sweat, while the massive Dana 70 rear end transfers all that power to the ground. They’ve added about four inches of lift with Rancho shocks at all four corners, giving it that perfect stance on custom wheels that screams “built, not bought.”

The cab keeps things surprisingly stock-looking with the rubber floor mat and original-style interior, though they did add power windows because why suffer when you don’t have to? e little details that separate a thoughtful build from a hack job.

This F-250 represents the ultimate sleeper truck - it looks like a restored classic but drives like a modern diesel with all the torque and fuel economy that comes with Cummins power. The 12-valve is legendary among diesel enthusiasts for its simplicity and reliability, making this Ford a truck you could actually drive cross-country without worrying about finding parts or a mechanic who knows what they’re doing.

The factory long bed configuration makes this more than just a show truck too. You’ve got real utility here, complete with the factory tool compartment in the bedside that Ford introduced in the mid-60s. It’s those original touches mixed with modern performance that make this build so appealing. You get the classic High Boy look that turns heads at cruise nights, but with the capability to tow your trail rig to the mountains without breaking a sweat.

This F-250 represents everything that’s cool about the current custom truck scene. It’s not about having the biggest lift or the most chrome - it’s about thoughtful modifications that improve performance while respecting the truck’s heritage. The fact that a Ford is running Dodge power just makes it that much more interesting.

You can check out the full photo gallery and specs on the High Octane Classics website. Whether you’re into the diesel swap scene or just appreciate a well-executed custom build, this Cummins-powered F-250 proves that sometimes the best combinations come from mixing brands that were never meant to go together.