Not an Epic but have converted my Canfield Riot and a friend's Pivot Mach 4. Used a Rohloff XC tensioner on both, big thing to keep in mind most tensioners that have enough range to handle chain growth can handle 19t-21t cog at most. The rohloff and the Melvin tensioners are tough to find right now or were a few months ago when I did the Pivot. The Rohloff will handle 21t but was tough to take wheel on/off ended up used 19t on both.bikes. have seen short cage derailleurs like Zee used as well, be nice to have clutch, but simpler to use SS tensioner.
Edit: the rohloff hub has a chainline 55-58mm, used raceface DM ring flipped to get +6mm to a place where the spacers that come with rohloff obtain correct chainline. Paul Melvin would be easier from that standpoint, but getting one was near impossible, but it looks like they are back in stock now