One of the nice things about talking to the Forge World designers, whether it be at GamesDay or the Forge World Open Days is seeing how they move models from ideas and drawings to concepts to finished product.
This Ork concept vehicle based on the Ork Trukk eventually became the Big Trakk.
The other side was more of a half-trakk opposed to the full tracked side here.
If you compare it to the Big Trakk model you can see how the model evolved.