The cover is signed "Simon and Kirby".
According to the Heritage Auctions note for the original art for page 3 of this story ( (http://comics.ha.com/c/item.zx?saleNo=121253&lotNo=10767&lotIdNo=18017), in the auction ending Dec. 20, 2012, the art is attributed solely to Joe Simon. The note states: "The image area of this drama-drenched page by the legendary Joe Simon.... From the Joe Simon Estate." Previously pencils were credited to Jack Kirby.