Chronology of Fanfiction: The Silver Age

March 1965 - Medusa
"The Frightful Four"
A re-imagined intro to Fantastic Four #36 (also available here)

July-August 1965 - Fantastic Four, Iron Man, Thor, Spider-Man, Hulk, Giant Ape and Monkey
"Bedlam at the Baxter Building"
A re-imagining of Fantastic Four Annual #1 (also available here)

May 1970 - Spider-Man
"The Specialist and the Schemer" 
A re-imagining of Amazing Spider-Man #84, mixed with the animated series.

June 1970 - Hulk
"The Brute that Shouted Love at the Heart of the Atom"
A re-imagining of The Incredible Hulk #140.

November 1970 - Spider-Man
"And Death Shall Come"
A re-imagining of Amazing Spider-Man #90.