We didn't hike Swallow Fork (not Shallow Fork - common mistake, I'll bet), so I can't comment on how hard it would be. I know there was a lot of elevation loss on Gunter Fork, so you'll almost certainly have to do some climbing. If it's overgrown like Gunter, it won't be fun. On second thought, Gunter Fork was one of the few trails in the area that is NOT open to horses, so that might account for it being so narrow and steep. Swallow Fork IS open to horses and just might be a real decent trail.
We met a group of 4 horsemen/women at the intersection of Swallow Fork and Mt Sterling Ridge trails. We showed them on our map which trails allowed horses. Saw horseshoe prints in the trail all the way to Laurel Gap.