Wobbly solebar

Here's a novel feature. When I looked closely at the solebars of this wooden model, the top edge of one wasn't flat and there is a bolt set into the face, sticking out the back.

A little bit of thinking and I recalled reading an old magazine where the idea of a rocking solebar was suggested as a way of compensating the chassis. It doesn't move much, only a millimetre at the extreme ends, but enough to deal with track irregularities.

The builder obviously had second thoughts as there were a set of rocking W-iron cradles in the box. That seems no fun, so I messed around with some brass bits to make a pivot point and found a suitable sized nut.

With the whitemetal axleboxes from the old banana van fitted (they are a bit long for a ballast wagon, but I'm not buying more), the wagon sits nicely flat and it runs well.

There is still a mystery - what were the bits of wood with a brass rod running between them intended to do?