Time to illustrate the progress so far. The picture below shows the transverse spacer .bar that I've put in to hold apart the two sides, and one of the slivers of plastic strip that I've inserted between the lead flashing and the wagon side. There is one on the nearer side as well - it is obvious that the Daywat used for sticking the chairs to this lead also dragged in the body planks as well.
In the background is an axle spacing jig from Bill Bedford. An excellent piece of kit, but not suitable for helping solve for problem that I found underneath this wagon. More later on that, and adjustments to both my thinking on this wagon, and rocking W-irons in general in my next post.