Religion among the 13th century Mongolian invaders was manifold, and with Kublai Khan encompassed Buddhism as a religion of state.
So if you wish to play in the late 1260s or 1270s, perhaps following the footsteps of Marco Polo and his family, you might think Buddhism over for your saga - with verrry little help from the ArM5 books. If you wish to make it a subject in your saga, you should have the PCs interact with Buddhist monks, though - and not just with Mongolian commanders following the religion of state.
People from the Mythic Europe of that time might use Friedrich II's handling of religion as a familiar model for religion under the Yuan dynasty.