The factory advised me that the landing gear cutout on the bottom skin needed to be cut back to the flange on "Wing Rib 12 ". My bottom wing skins are an early version. ( later ones have been modified.) The test fit yesterday confirmed that the modification definately needed to be done. The cutting of the lower inboard skin was much easier than I expected. With the assistance of CJC, AEC, KSC, and "Jonesy" ( Christophers mate ) we moved the wings into the build shed so I could modify the lower wing skin. To all Sling 4 builders ensure the skins have been cut correctly, if not it was very easy to fix.