Check skins upon cleco'd HS frame. Discovered that the main spar assembly on the port side was just a wee bit short. This made the tip rib not 90 degrees to the structure and would ultimately make the ribs differ slightly from the pre-piloted holes in the skin.
Remade T03-06 (the offending part) from sheet. Drilled out original piece.
Deburred, acid etch, allodined all remaining parts.
The tip ribs have the flanges going the wrong way. Easy fix.