There is no indicia, no date (not even a copyright statement), and the only reference to Marvel is the MC on the cover. According to the ad on the back cover, this is part of a set of four Marvel books and two DC ones. One of the DC ones (Superman) has a 1966 copyright date, so that should place this book also in 1966. These sets are listed as available from Golden Records, 250 West 57th Street, New York, NY 10019. In that ad this book and record set was offered for 2.49 USD.
First appearance of Thor, Don Blake and Gorr, origin of Thor.
Pages are renumbered to follow the numbering from the first story.