Whatever it is, it's pretty cool.

JM, when you go visit it, can you take some photos of how the engine/transmission/rear case was integrated to the frame assembly. I can guess at what it is, but the interesting pieces for me are in the detail of how they worked around the various obstacles. Based on the way the Vickers unit that is at chumduffy's place operates, the tractor pivoting could be quite severe if the operator steered too aggressively. If it was going to design a unit like this, I think my approach would be to combine steering clutch disengagement along with proportional steering in the articulated section. In which case, swapping the bevel gear arrangement for a differential would be a possibility if a suitable diff could be identified