As I said on the old DC message boards, both BATMAN No. 192 (June '67) and GREEN HORNET No. 2 (May '67), given the vagueries of distribution in the '60s, happened to come out at the same time in my neighbourhood. Both these comics featured a story set in Chinatown, with similar Chinese characters. So, even though Batman and Green Hornet never met in those stories, this was my unofficial comic book crossover.
By that time Batman and Green Hornet had already crossed paths in "A Piece of the Action"/"Batman's Satisfaction" (broadcast on March 1st and 2nd, '67)--so I was ready to believe they could meet in the comics.