Same here, Taeylor - I read something about the Stairway on this forum before I ever saw the actual episodes, and I was immediately intrigued. Frank's book sounds fascinating, and you can get a good preview of it on amazon.com!
"Dark Shadows"'s first trip back in time was Barnabas in 1795, and Gothick once proposed that the movie "Berkeley Square" was an influence on the DS writers. I have read the play and enjoyed it; it was also re-made into another movie that I've mentioned here before, "I'll Never Forget You" with Tyrone Power. "Berkeley Square" in turn was inspired by an unfinished novel by Henry James. I suspect that James himself was influenced by H.G. Wells, with whom he corresponded and was on collegial terms.