I completed each Wing Box prior to attaching the Skins. For the most part the wing skins were pilot hole drilled but the Ribs and Spar are not pre-drilled.
First the skin can be alihne at the Aft Spar and Main Spar and clamped in place for drilling through the Spars. The Main Spar alignment and drilling is very important so that you get the right placement of the rivet in the forward edge of the Spar.
The objective is to locate the skin so thet the holes line up with the center part of the the Rib edges. To accomplish that I marked a line down the center of each Rib edge with a fine point sharpie. Then aligned each rib one by one so that I could se the line through the pilot holes of the skin. Then drilled and clecoed down the Rib starting at the Main Spar. I could not think of a way to clamp these in place so having a second person to help hold the Rib in place is important. You would not want twists in the Ribs.
Later when the Forward Leading Edge Skin is installed the hole in it will have to align with the Aft Skin holes at the Main Spar attach point.
Since both these Skin parts were pre-drilled I had no problem lining them up.
