I am not all to familiar as well and would like some expert thoughts on this subject.
I do know these couple of characteristics should be taken into account for a fact:
- make sure both ends of the endlink is able to full able to rotate up (towards the top of the car) and down (towards the bottom of the car) and is not centered/biased/pointing towards either aforementioned directions. left and right (towards the front and back of the car) is not
as important because swaybars dont move on that axis
- make sure both faces of the ends of endlinks the "O" that holds the ball are 90deg perpendicular to each other. see the last 3 pictures on the bottom
http://cdn.splparts.com/tech/SPLFEZ33.pdf
- swaybar should be as parallel to the car as possible. this is for full utilization of the bar.