I too have read the Wescott book about the G&D more than once. A few years ago, I loaned my original one to a guy, and (surprise!!) he never returned it and I have since moved away. So in September, I bought another copy, used of course, in pretty good shape.
I have incorporated a few of John Allen's ideas in my layout, including the use of mirrors to fool the eye into "seeing" more depth in a scene than is really there. He was a genius, and really turned the "train set" into the model railroading hobby we have today.