Ages ago, I believe I actually read the article that pitched the GS&S Ry, I believe in a book put out by Kalmbach that was in my local library. It always struck me as an interesting concept for a fun small layout. I wondered what others thought about the concept, and whether or not anyone had translated it into O Scale? As I recall the layout really puts a limit on train size. However I think there are a lot of good choices for small switchers in our scale now (Docksider, Porter, Plymouth ect) and rolling stock, esp Lionel's latest forays into logging equipment that would make this layout feasible.
About the only thing I'd change if I were building this thing would be to modify the lower yard so that there was only one switch, oriented in the same direction as the other switches so that you could better set out or pick up cars before climbing the switchback.