Interesting mention in Quentin Tarantino's novel of "Once Upon a Time in Hollywood"

In a segment giving backstory to his protagonist, Rick Dalton, Tarantino writes that this movie was originally written as a Magnificent Seven sequel and called "Cannon For the Magnificent Seven". The producer cast George Peppard as "Chris", the leader of the Seven, because he was a bigger star than George Kennedy, who played him in Guns of the Magnificent Seven (replacing the original Chris from the first two, Yul Brynner)

Peppard refused to be the 3rd guy in the 4th movie to play Chris and demanded they remove all references to The Magnificent Seven. He got his way and the story was altered.

I am not sure if the basics of this is true, or if Tarantino made it all up.