In advance of the inevitable annotations: I've managed to work out that "Vull the Invisible" was a serial written by Temple Murdoch in The Ranger circa 1935, but apart from that nothing further. Can anyone point me to further info?
Also gotta love that metafictional namecheck for Guntag Borghelm, the Shazam-surrogate from the original Marvelman comics (subsequently retconned by Moore himself as a fiction created by Emil Gargunza).