One of the best parts about writing a period piece with a public domain character is the chance to create a kind of "shared universe." Alan Moore did this in League of Extraordinary Gentlemen, and Philip Jose Farmer (and by extension, Win Scott Eckert) created the Wold Newton Universe. In GREEN LAMA: UNBOUND, aside from the obvious Green Lama/Cthulhu Mythos crossover, there are several pulp and movie cameos that weave through the novel. Here's a shortlist of the non-spoliers:
-Captain Hazzard is referenced and makes an appearance as one of the Green Lama's pupils. He also indirectly provides the Green Lama with some much needed aid.
-Lance Star, Dan Fowler, Jim Anthony are all referenced by Jean. All of whom have stories published by Airship 27.
-Atop the Empire State Building, Caraway recalls the "rampaging ape" that was killed there.
-The Nazis reference the Toht and Vogel embarrassments.
-The character Rick Masters originally appeared in back-up stories in the Green Lama comics, and only first made his pulp appearance in Kevin Noel Olson's "Shiva Endangered"
-The serial Undersea Kingdom is referenced, partially as foreshadowing.
-The term "color out of space" is used.
Believe me, this is only the tip of iceberg.