IC: Pendragon with variant setting
Keep the rules the same, but use a more historical setting. I was thinking the Christianization of eastern Europe as a backdrop because it would allow a similar Christian/Pagan conflict. Could also use more Slavic-type mythology for supernatural encounters. (Also, I am a little partial because I am of Polish descent)
On the other hand... including real religions and real historical conflicts (albeit fictionalized versions of them) may be a little problematic. Though, both Ivanhoe and The Teutonic Knights have prominent Christians as the main villains.