DC and Marvel did not officially team up until 1975, but they've always enjoyed chirping each other, and in JLA #103 (1972), the Justice League battled a demonic force that possessed the bodies of some Halloween masqueraders.
The costumed individuals, though not directly identified as their Marvel counterparts, are obviously intended to be Captain America, Spider-man, and Thor. The issue also features the first DC appearance of Captain Marvel. DC had just acquired the rights to Fawcett's super-star, and he, too, appears as a powered-up party-goer. The issue ends with the DC's announcement that the Big Red Cheese-- whose career they'd ended with a lawsuit, claiming that he infringed on their copyright to Superman-- would soon reappear in DC continuity. Jay Pinkerton has an amusing piece about this issue here