For future reference, here's the link to the other thread:
http://www.tractiontalkforum.com/showthread.php?t=36924
My impression of the scrapyard photo (repeated below for convenience) is that the wagon was effectively sticking out of the side of a large pile of scrap, and so while it was accessible to take a photo, it might have had many tons of scrap that would need removing to retrieve it. As Dad mentioned, John Butler tried to buy it at the time, but was unable to, and by the time Tom purchased the remains, the wagon had been much more heavily cut up.
One possibility to consider for a replacement steering box might be seeing if one could be fabricated from plate, instead of making new castings. From the photo, it's flat sided, and the curved part of it only curves in one direction. I know Julian Hopper in Kent has made some very complex fabrications in the past for other steam wagon projects. Obviously the worm and wheel (or worm and segment) are still a problem, but it might solve part of the issue.
