“Writing for a musical is a marathon, not a sprint,” says Zach Chance, one-half of Jamestown Revival, the folk duo behind the music for this season’s stage adaptation of S.E. Hinton’s novel The Outsiders (with Justin Levine). “You have to be able to re-approach the work over and over, to be unafraid to look at it honestly.” Jonathan Clay, the other half of the band, is just as circumspect. “It’s like writing in 3D,” he says, referring to the ongoing collaboration between performers, designers, the director and the choreographer. It helps that both singer-songwriters love the source material, about rival gangs in 1960s rural Oklahoma. “It was actually the first novel I ever read,” recalls Clay. “Decades later, the story is still just as good.”