Manuals are notoriously bad for photos, the people making them don't usually know the item or subject. In addition, they are often very early -- I've even seen manuals with commercial illustrations. One NM manual has an arrow and label pointing to the wrong part.

If you twist the light rifle in the photo so that the toe is on the radius from the center, the sight will contact the barrel. Then pull it outward until the sight locks over the barrel. Making a stack by yourself is hard, SOP is three people.