Harris confirmed as editor per his biblio in Robin Snyder's The Comics!, Vol 29, No.5, May 2018.
On sale date is Library of Congress copyright record publication date.
Bullwinkle previously appeared in Rocky & His Friends (Four Color #1128) (first appearance), Rocky & His Friends (Four Color #1152), Bullwinkle and Rocky (Four Color #1270), and Bullwinkle Mother Moose Nursery Pomes (Dell #01-530-207, May-July 1962). After this issue, he appeared in a new series (Western, 1962 series).
Based on the 1959-1964 television show that had two different titles in its original run ("Rocky and His Friends" and "The Bullwinkle Show") and several more titles in syndicated reruns, but is known now as "The Adventures of Rocky and Bullwinkle and Friends".