Work-in-progress 1951 GMC Duramax Swap

Andrew Calkins is used to doing things a little bit differently. That’s why his personal cruiser is a 580-hp big block ’70s Dodge Demon. For a parts hauler, he decided again to break the mold. “I just couldn’t put an LS in it, so I started looking for alternatives,” he says. If you couldn’t guess by looking at the big block in the A-body, Calkins enjoys torque. So when he found a wrecked GMC with an ’06 LBZ Duramax, he jumped on it.

Even though his swap vehicle was a truck, Calkins knew he couldn’t just drop the engine in. “I wanted the truck to handle like a new vehicle, which meant I couldn’t keep the stock front suspension, and it wasn’t up to the task anyway,” he says. He also was a bit choosy about his engine location: “I wanted to keep the stock body lines, and stock(ish) firewall, which meant that I had to cram as much as possible in quite a tight space.”

With the cab up, you can see the immense amount of work that has gone into making a smoothed firewall for this GMC. Luckily, since Calkins is a fabricator at Vintage Hot Rod Design and Fabrication in Chico, California, he was up to the task. Calkins figures that building a molded firewall around the engine involved a solid 60 hours of labor.


The front suspension on the GMC is made up of Crown Victoria A-arms, steering components and brakes. Calkins says the beauty of using coilover shocks for the conversion is that the front spring rate can easily be adjusted for the correct ride height.

Like many folks, Calkins started with a donor truck. “There was an ’06 LBZ that was a rollover, and by the time I got to it the axles were out of it too,” he says. What was left was the engine and transmission, which he was more than willing to secure for his ’51 GMC pickup. Calkins was able to pick up the complete engine and transmission, as well as the gas pedal, the ECM and most of the wiring.

“The ’51 that I have is a pretty solid truck,” Calkins states, and he didn’t mean just in the cab. The entire frame was in good shape, and he was willing and able to reinforce and box the frame where it was warranted. The front suspension was a different story, however. He wanted the truck it to handle, and it had to support the weight of the Duramax engine, so his choices were slim. He knew police cars are usually built like tanks, so he ended up using a combination of newer Crown Victoria and Mustang parts to make things work. The rear suspension will be a triangulated four-link that will use a modified 9-inch rear axle.

Calkins is very forthcoming about the fact that he has a long way to go. “I still might change my mind about the suspension, or the transmission, or who knows what else,” he admits. “But I have a start, and I know in the end having a 500-hp, 30-mpg parts hauler is going to be worth it!”

Calkins fabricated the front frame himself; there was no “kit,” so he says he just started welding. The front section of the frame is boxed for strength and to support the weight of the diesel engine.
A big part of the reason for the front suspension swap was so that Calkins could use a tiny Ford Explorer steering rack instead of a huge steering box. As with everything else, he fabricated the mount himself.
Calkins mounted the ’06 Duramax engine on the frame by using a combination of small block Chevy engine mounts and a set of homemade adapters.
The barley-visible transmission is a 4l80E that Calkins said bolted right up. He was even able to use a converter cover from a 4L85E transmission out of a Chevy Express Van.
It’s important to keep motivated, so Calkins has already polished up the engine in the truck and added some trick valve covers from WC Fab. He says his buddy (coincidentally also named Andrew) will be in charge of the engine wiring and tuning.


The rear suspension is still filed under the “to be determined” category, as right now the rear axle is just tack-welded to the frame so the truck can be moved around. The rear is a pretty stout 9-inch with a Detroit Truetrac posi, aftermarket axles and 4.11 gears that Calkins plans to swap to 3.25 later on down the line.
Some of the factory engine had been rusted and damaged, so Calkins updated the Duramax by using an LML front cover and oil pan. Since he did the frame fabrication himself there were no clearance issues.


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