Nothing quite like that, though I have thought of plots and character ideas and written notes; but never a full on story.  I had ideas for a generational look at heroes, mirroring the eras of comics and thought of a superman, born of Atomic Bomb tests, with an ultra-conservative American hero type, as part of it; and, lo and behold, James Robinson turned out The Golden Age and there was that plot, with some twists that never entered my head.

I do have a vision of a Sgt Rock and Sgt Fury crossover, during the Battle of the Bulge.  It just seems to me it would have to be at that point.  Rock and Easy are part of the defenders of Bastogne and Fury and the Howlers finagle their way up there to help stop the Germans.  i even had the idea of them defying orders, gowing over in a plane, flown by a maniac pilot (Blackhawk) to do a parachute jump into the the town, with some supplies.  I see them jointly running aggressive patrols to harass the Germans and fool them into thinking there is a counter-attack, holding them back from advancing further, until Patton's relief forces arrive (with the Haunted Tank in the vanguard).

I've written tons of fanfic about all this stuff!