If I may, wouldn't it be better to use Jesse James as a replacement for Gol D. Roger? I know Billy the Kid is an easy to identify name but James and his gang were more prolific robbers and James also (somehow) earned a reputation for being a sort of Robin Hood-like figure, which serves to further inspire people. Also gives you a nice possible antagonist in Robert Ford, who in this universe likely sold James out and got himself a nice position in the world government. Uh, I'm interested in case you couldn't tell.