Jay, the magic isn't so much with the 3d printing, as with the 3d modeling 
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The trucks used on the sdl39 are quite different from the HTC-1's. I believe they are a design for export locomotives, so while they are somewhat similar to EMD Flexicoil 3 axle trucks, there are any number of distinctions. The trucks are often the most difficult aspect of any sdl39 build, due to their unique style.
For starters, the wheelsbase on the sdl39 truck is 12'-2", versus 13'-7" for the Flexicoil or HTC-1. There are also differences in the truck castings, some subtle, some obvious. Some of the detail parts are common to other EMD trucks, like the journals and brake cylinders, so those parts wouldn't be an issue.
There are versions offered via Shapeways, although I only know of them in HO scale. The usual caveat applies about contacting the owner and requesting O scale versions. O scale frames may already be available, but I've never looked for them in particular to know one way or another.
If you expand your search beyond manufacturers for North American prototypes, you will find manufacturers who have done the trucks for export locos. Again, they tend to be HO scale. However, it may be worth an email or two to ask for help, or availability in O scale.
In the worst case scenario, given sufficient information, an accurate 3d model of the side frames can be produced, which can then yield masters for casting, as Jay suggests. In fact, 3d prints could be used directly if they weren't load bearing. However, in my experience with this sort of piece, with the inherent detail, the common materials available for printing are fairly brittle and not particularly durable. So in my opinion, a brass or resin casting, or hybrid casting/etch combination, would be more ideal.
Everything else besides the trucks will be a matter of scratching or bashing common EMD parts to match the prototype.
Good luck!
Jim
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