While I was playing with the flaps, I made a first attempt to center the control sticks by adjusting the rod end bearings of the aileron control rods.

Getting very close to 90 degrees. It 's almost impossible to get this perfect on 90. half a turn on the center pushrod moves it too much to one or the other way. This is as close as I could get it for now.

After a lot of try and error work, I finally finished the flap actuator hole in the fuselage side skin. The flap moves freely to the full up and full down position.
Using key files and a dremel with grinding wheel, I managed to make the perfect shape.
Move a little at a time, insert the pushrod again and move the flap a bit lower which will move the actuator to front and outboard. Mark "where it wants to go", and file a bit more. Then try the same thing again until you reach the full flap angle.
To save some time, I taped some transparent plastic on the hole and marked the contours to be copied on the other side.
I wasn't planning to do the full cut based on that but it would give me a very good idea how and where to make the first cut on other side

 bottom view

 In the next images, I transferred it on the other side showing where the hole has to be made.

side skin