St. John did the cover paintings for the first two installments of Jack Williamson's “Golden Blood,” for the April and May 1933 issues of Weird Tales. The third and final installment, which appeared in the June issue, gave the cover assignment back to Margaret Brundage for her depiction of a scene from "Black Colossus" by Robert E. Howard.
St. John also did interior illustrations for all three installments.
In 1978, Tamerlane Press publish the book in hardcover, and used the original artwork from the April 1933 issue for their dustjacket. A portion of the cover from the May 1933 issue was cropped and printed in brown for the endpapers.
I located more discs of scans of St. John postcards. These were scanned over 15 years ago, and aren't the scan quality I would use today, but they should still be fine for this purpose.
Here is the front and back of a 1904 brochure St. John did for The Osborne Co., of New York. The Osborne Company was a publisher of calendars and art prints.