ORIGINAL: ballgunner
There used to be some control horns made especially for the movement of Fowler type flaps. To me that sounds similar to what you are trying to do. Investigate the possibility of having the control horns do the work and then adjust your servo arm throw accordingly.
don't need special gadgets to do a semi-Fowler flap.
This is how I hinged the flaps on a Kadet Sr. Note the pushrod pushes and pulls the LE of the flap, not the control horns being used as the hinges. worked VERY nicely.