Someone here with a 1985 calendar and a good grasp of DC's publishing schedule credited the Swamp Thing team-up ('The Jungle Line'

as the very last pre-Crisis appearance of the Silver Age Superman. (I still anticipate his first post-Crisis appearance. He's out there somewhere. I just know it.) 'Jungle' was written by Alan Moore, who did 'Whatever Happened to the Man of Tomorrow?'a few months later.
'Jungle' is an outstanding story, one of the very best ever, and again gives the lie to the idea that compelling stories about the supposedly godlike Silver Age version of the character couldn't be written, yadda yadda yadda.