The first film in the series, Seven Men from Now, was produced by John Wayne's production company, Batjac. The story and screenplay were the first ones written by Burt Kennedy, who would go on to help write (screenplay and/or story) five of the movies in the series. Westbound wasn't written by Burt Kennedy and wasn't produced by Harry Brown but it did star Randolph Scott and was directed by Budd Boetticher,
In each movie, Scott plays a loner who just goes about doing what he feels he has to do, even if he doesn't really want to. There is also usually an adversary who he admires, and who admires him.
Most of the movie have very similar plots and even use some of the same dialogue. It looks like the team was tweaking little things to try to get the story right.