Originally Posted by Geekage

Yeah, but it's a bit of a hack getting horizontal dropouts and disc brakes to coexist.

The Surly horizontal dropouts need to have slotted IS disc brake mounts so the disc caliper can be slid back and forth depending in the wheel position. Actually, slid and rotated.

Of you just need to tweak the chain tension, you probably don't need to readjust the disc caliper position, it's probably close enough. And on the plus side unlike with Alternator dropouts or eccentric bottom brackets, you just need deal with the wheel nuts, not the dropout or BB pinch bolts.