This is one of the most incredible models I have ever seen. Brett Gallant- Sierra West Scale Models, produced a dynamite HO kit of this a few years ago, and Karl Allison is doing a scratchbuilt version in O scale. He is doing a build-thread on Brett's SWSM forum if you want to follow along:
http://www.craftsmankituniversity.com/vanforum/index.php?p=/discussion/323/the-loco-and-service-shops-scratchbuilt-in-o-scale#latest (http://www.craftsmankituniversity.com/vanforum/index.php?p=/discussion/323/the-loco-and-service-shops-scratchbuilt-in-o-scale#latest)
A good synopsis of the photos to date is here on Mario Rapinett's great Modvid site. You won't believe the details:
http://www.modvid.com.au/html/body_karl_allison.html (http://www.modvid.com.au/html/body_karl_allison.html)
Cheez....is all of that machinery scratch built?
You're right....the detail is unbelievable. You could literally count rivets and gear teeth if you wanted to.
Fantastic.