Placed the wing tip rib into the left wing tip and drilled the trailing edge hole on each side after laying out the rivet hole locations on the wing tip. Re-installed the tip onto the wing using clecos to hold it in place.
Carefully adjusted the rib with the trailing edge holes clecoed so that the face of the rib was flush with the trimmed edge. (Trying to site the center line at the front edge was futile.) Drilled the rivet holes through the wing tip and into the rib and clecoed each hole as drilled, starting at the trailing edge and alternating top and bottom while checking for alignment of the face with every hole drilled.
With 2 holes left to drill on each side, it became too difficult to confirm proper alignment so removed the wing tip from the wing and drilled the remaining holes on the work bench.
Counter sunk each rivet hole with the rib clecoed in place. Removed the rib and deburred.
Ribs now ready to rivet in place when I have a helper available.