Narrated in the first person. This story is divided into two parts: an untitled part one (6 pp) and part two—"Gargantus" (7 pp). Story is pages 3-7, 10-14, 16-18 of comic (pages numbered 1 to 13).
Gargantus last appeared in issue #80 (January 1961); he next appears in Marvel Monsters: Monsters on the Prowl (Marvel, 2005 series) #1 (December 2005).
Text story with illustration. Text story is pages 8, 26 of comic (pages of story not numbered).
This story is retold in Tales of Suspense (Marvel, 1959 series) #48 (December 1963) as "Kraddak" by Stan Lee and Larry Lieber. Possible Lee plot and Lieber script per Nick Caputo. Previous indexer credited Stan Lee solely.
Story is pages 20-24 of comic (pages of story numbered 1 to 5).
This story seems similar to "Gorilla Man" drawn by Robert Q. Sale in Men's Adventures (Marvel, 1950 series) #25 (March 1954).
Possible Lee script per Nick Caputo's examination at his blog:
http://nick-caputo.blogspot.com/2011/11/who-authored-ditko.html
Story is pages 28-32 of comic (pages of story numbered 1 to 5).