I have been re-reading The Widow's Son, and as I read the footnotes I sensed that Wilson had mixed in a nonexistent book, Golden Hours by de Selby, amidst the real books he mentions. A few Internet searches established that not only is Golden Hours a fictional book, but it's a fictional book invented by another author, Flann O'Brien, in his novel The Third Policeman.
I asked Eric Wagner for more information, and he kindly replied. "De Selby shows up a character in two of Flann O'Brien's novels. Bob used the De Selby character in The Widow's Son and elsewhere, but he got scared the O'Brien estate might take action against him, so he changed the name to Timothy F. X. Finnegan in later works."