inside front cover
Giant Comics Editions (St. John, 1948 Series) #12, a book made up of re-bound cover-less St. John publications, has as part of it's contents a coverless Adventures #1. That section contains 32 pages and does not include the original comic's covers. The last story (The Black Lily) ends at an odd spot, almost implying a finish on the inside back cover.
Writer and art credits confirmed by Starr in Alter Ego #111 (July 2012).