Whether the drag link is above or below the line of being level doesn't matter...especially for a front end designed like the AD. If we had a track rod or track bar that was a different length than the drag link then we could have all sorts of different bump steer problems. Those have different pivot points and thus different arcs and all sorts of "arguments" can happen. Our front end works more like a simple 4x4. We just have a solid axle, a tie rod and a drag link so the drag link makes the arc. To minimize bump steer the drag link has to hit the center (parallel). You can see it...very easy to visualize. The higher point on the arc of the circle will have the same effect as the lower point and the higher/lower on that arc the point of intersection is, the more bump steer will occur because just a little movement will pull/push the drag link in an exaggerated manner.
With the spring anchored to the frame at the rear, the steering knuckle will travel in an arc whose center it at the spring anchor point, an arc modified by the fact that the other end of the spring is anchored by the spring shackle but it will travel in some form of an arc nonetheless. I expect that when GM engineers designed the front suspension they chose spring lengths and center points so that the arc of the knuckle would match the arc of the drag link as closely as possible. That would minimize bump steer. Of course the arcs cannot be identical because the pitman arm center is a foot or so above the spring anchor and forward of it.
I note that some old heavier GMC trucks had the fixed point at the front and the shackle behind. However, I don't remember if the drag link ran backwards toward the knuckle with the steering box ahead.Maybe those were cabovers but memory is fuzzy.
