I'd recommend finding religious studies programs that have faculty who employ literary perspectives. I'm sure you can find scholars who focus, say, on the literary composition of the Book of Job or Bhavagadgita or medieval Islamic poetry. I wanted to give examples from different religious traditions to cast the net wide but you can let your interests help you narrow the focus on the right scholars/program. I'd also imagine it'd be a great plus to have profeciency in a research language other than English. I'd think there would be plenty doctoral programs in religious studies that would be open to applicants with a BA or MA in literature and no MA in religion.