The Avengers #125 (1974)

Earth's Mightiest Heroes blast off into outer space to intercept Thanos' awesome armada headed towards Earth! The Avengers attack the alien starships and inflict heavy damage until they bump into a solid black force field! They are able to penetrate the force field and discover the mad Titan's massive command ship with hordes of aliens inside! So they disable the ship's universal translator and throw the entire attack fleet into chaos! Have the Avengers finally derailed Thanos' plan for conquest of the cosmos? Yeah, right!  Guest-starring Captain Marvel.  Written by Steve Englehart. Art by John Buscema (breakdowns) and Dave Cockrum (finishes). Cover by Ron Wilson and John Romita.

Key book: first cover appearance of Thanos, the Mad Titan. Note: The Marvel Value Stamp series A #69 Marvel Girl was removed by 11 year old me. Fair condition.