This one took me a bit by surprise. About a year and a half ago, I wrote a post about Action #331 (December 1965), where the story concerned Lois Lane writing an article for the Daily Planet about how Clark Kent was really Superman. It was intended as a gag, but the pressman who ran off a few copies took ill, and his assistant accidentally ran off the full press run with the headlines. At first it appears that the Planet will suffer, and Lois will be fired, but then Clark suggests that if he pretends to really be the Man of Steel for a few days and then the Planet reveals the gag, readers will forgive them. Inevitably this causes big complications, but in the end it all comes off well.
It turns out that this story is virtually note-for-note swiped from Superman #20 (Jan-Feb 1943). Note:
Oh, there are a few changes here and there; "Ironjaw" the villain becomes "Iron Ike" and some of the more humorous slapstick moments of the original like these are gone:
But overall this is one of the more blatant Super-Swipes that I can recall.
The Superman #20 story is contained in this archive edition: