Drilled upper aft skin to the RH wing spar and ribs. One slight issue with the leveling - when the wing spar/ribs assembly is set top side up, placing the level from the aft spar to the forwards spar works fine at the outboard end of the wing. At the inboard end, the angle of the main spar cap lifts the level maybe 1/16". I thought the wing would just be warped by that amount, since this is how I did the other wing, but after turning it over to do the lower skin (and lock in the washout), the level sits nice in both the outboard and inboard locations. Really not much to setting up the wing for no twist. Simply blocking it up on a table works fine. The centerlines on the ribs from aft to forward spar ensure the aft spar is correctly located inboard-outboard relative to the forward spar. The straightness of the aft spar relative to the aft edges of the skin gets the skin all squared up in that direction. Then all you need is a level at the inboard end and outboard end of the wing between the aft and forward spars. The table doesn't need to be level. The two ends of the wing don't need to be the same height, just forward to aft being level to give no twist - and the twist is only locked when the second skin goes on. (Get it as close as possible for the first skin, but it's not locked until the second one goes on.) I know this because I turned over the one-skinned wing on my own, and it will twist a good 4-5" from tip to root with only the one skin in place.
