Quite a few small self-propelled cranes used standard trucks, or at least standard sideframes. They would have a chain, belt, or possibly shaft drive to one or more axles, not easily visible from the outside.
Many years ago, some south Texas narrow gauge did that with a wooden boxcar. They put a gasoline engine in one end, ran a chain (if I remember right) to one axle of the front truck, and cut windows in the end for the crew.