After work today I straitened and fluted the HS-404 and 405 ribs and then re-installed and clamped them into position on the left side of the horizontal stab, before back drilling with a #40 drill, I then back drilled the entire skin top and bottom in the sequence suggested in the instructions. Next step disassemble, debur, dimple and prime and and .....
HS-405 clamped ready for back drilling
HS-404 clamped for back drilling
Skin back drilled, wow the structure gets strong once the skin is in place.