The shaper fence will work fine for overhead routing. If you’re milling the entire edge off of your workpiece, that would be the way to go, as the two fence halves are independently adjustable.
If you’re starting with a straight edge on your workpiece, you’re not milling it all away, and you can make the cut in one pass, you could use a bearing-piloted router bit without a fence.
You can also easily make an auxiliary routing face for your rip fence. Just attach a flat board to the side of it, and bore a vertical hole in it large enough to fit your router bit. The hole should break through the side opposite the rip fence. Then adjust your fence to control how far the bit protrudes beyond the auxiliary face.
Power Tool Woodworking for Everyone gives more detail in the routing section. The shaping section covers the use of the shaper fence.https://www.shopsmith.com/academy/routing/index.htm