Answer:
The two main differences between King´s story and the film adaptation are who takes the gun to threaten Ace and his friends, and what happens to the main characters when they grow up.
Explanation:
In King´s story, when Ace and his friends get to the place where the main characters have found the body, Chris threatens them with the gun, while, in the movie, it´s Gordy who does that.
At the end of the movie, Gordie (voiced by Richard Dreyfuss) describes what happened to his friends afterward. While Vern ad Teddy stayed in town, Gordie becomes a writer, and Chris gets to be a lawyer. Sadly, Chris dies. This is different from the book, where Vern and Teddy also die at a young age.
