Crossover Cover: Spirits from Beyond

I am currently reading the fourth book in Simon R. Green's Ghost Finders series, and so far there have been a few crossovers. The Drood family (from Green's Secret Histories series) and the Nightside are mentioned. At one point, the Carnacki Institute field agents visit the Institute's Secret Libraries. The Empty Librarian, so called because he appears to be a talking empty suit, tells them that the Libraries' Index, which is bigger inside than out, was made by the Traveling Doctor. In Green's fiction, the Traveling Doctor is the name used to refer to Doctor Who. Among the items in the libraries are the Siggsand Manuscript (from William Hope Hodgson's Carnacki stories, although there it's spelled "Sigsand"), a single marble finger (from E. Nesbit's story "Man-Size in Marble"), a brass mezzotint (possibly a reference to M.R. James' story "The Mezzotint"), and the Sword Sacnoth (from Lord Dunsany's "The Fortress Unvanquishable, Save for Sacnoth.")