16.5x24.5" cardboard box proof (not a box flat) for 1970 cereal box that had back panel promoting offer for the first Kellogg's baseball cards issued, "3-D Baseball Cards" that were available one per box. Set of 75 cards was also available by mail order. Nine example cards are shown - Tom Seaver, Roberto Clemente, Reggie Jackson, Ernie Banks and Al Kaline among those of note. Proof has some scattered handling wear w/a few creases at corners, but would look great framed. Rare proof.