I discovered the existence of this novel in 2019 when browsing The Crime, Mystery, & Gangster Fiction Magazine Index for details about Dan Malcolm stories. I'm pretty sure the cover was originally in color, but haven't been able to find an image anywhere.
Other resources
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Acknowledgements: Robert Silverberg for cause, support, and cooperation; Ken Seamon for graphics; Rodney Walters for books and info; Alvaro Zinos-Amaro for comments and content; and all the fellow fans who have sent encouragement, information, and translations.