Marked bottom stiffeners and drilled holes. Marked trailing edge holes to be ��om skin trailing edge, and leading edge holes to be �from end of stiffener (3/8" from spar). Remaining holes equally distributed using a rivet fan. Fabricated top stiffeners and drilled holes. Laid out lines for positioning top stiffeners. Drilled stiffeners to skin and clecoed in place. Had to fabricate one new stiffener – mis-drilled first hole in middle top stiffener of right elevator by approximately 3/32"” -- had to relocate entire stiffener. Should be almost unnoticeable.