Understandably, vicious has not released any of the actual cad files besides a dxf of the motor mounts and maybe a beta part here or there.
However, you have some options to use the stl files on thingiverse. Autodesk offers the full Inventor Professional to students. You could download it and do the assembly and then be done with it (or activate if you are a student). Inventor Pro 2017 actually handles stl files really well in assemblies. It can even give you an axis through a hole to constrain to. If you get an older version you can use the Autodesk Mesh Enabler, an add in for inventor, to convert the stls to a base feature. But the assembly will be sloppy at best.
Have you tried just converting the files in solidworks? I think he uses solidworks to create them. I had great success converting some step files at work in solidworks to sldprt files and using feature recognition. It even managed to give me the sketches, holes, and tap sizes.
Edit: had no luck easily converting to a sldprt in solidworks 2015. But at least you get what the mesh enabler can get in inventor. A ton of triangular surfaces. You CAN mate to them, but I wouldn’t rely on any exact measurements from an assembly assembled that way.