Question

What would the novel A Separate peace be like if Finny narrated the story?

Answer 1

The analyses of these characters should help you decide how the point of view would change -- what he would tell, how he would describe other characters and their actions, etc.

http://www.sparknotes.com/lit/separate/canalysis.html
Gene (the actual narrator) and Finny are the first two characters analyzed here.