That looks like a pretty nice bike, have you seen it in person? Mountain bikes get beat up, so what kind of shape is it in and does it fit you? What's that old saying...something is worth what you are willing to pay pay for it.

As you've already noticed, this place is geared to roadgoing SS/FG and outside of a few, not much real mountain biking knowledge here. But Bikeforums does have a mtn bike subforum if you look for it - bound to be some singlespeeders there who might be able to help you.

Have you not found MTBR? They have a very active SS forum there.

Not to split hairs...but Surly 1x1 is actually more of a singlespeed that can, of course, be set-up fixed. Had one, excellent bike, occasionally rode it fixed on MTB trails, which is a great way to to sharpen one's skills and make going slow both challenging and a lotta fun!