[shovel]

If I had to speculate on the suspension I'd suggest it's a trailing arm using the beam's torsion (or a separate, interior beam's torsion) as its spring. The beam itself may not be fully circular, lending a plane on which it can resolve torsion. That doesn't resolve the question of damping however, maybe an internal fluid shock? Possibly some trick of mass, where the whole assembly is so light that it can't pick up any road harmonics at any realistic speed so a fluid damper is almost unnecessary?