Again, I see some comments in some of the above posts that are not really correct. As one who has been setting up pull-pull on both elevator and rudder on dozens of large (1/4 scale or larger) with success, I will just mention some of the false statements.
You must always have equal lengths on the servo and on the horns on the surface: definitely not true, what you have to make sure of is that the degrees of rotation of the driving arms does not travel so far that the moveable surface horns are rotated past 180 degrees. i.e. as long as the surface being moved does not move past the point where the non pulling line starts to tighten. It is easy to demonstrate this with a compass and a sheet of paper, just draw the respective arcs and measure the distance between the fixed points on the arc for different degrees of throw.
You must always have the attachpoints at right angles to the hinge points of the surface being moved: again false, what you want is to have the attachpoint offset from the hinge point (that is how you get the desired positive Ackerman effect). Realize that if you get the attach point on the wrong side of the hinge point you will get negative Ackerman which can be very bad as both lines try to tighten as you move the surface away from neutral.
You must have straight line shots between the servo and moveable surface: again wrong, if you use the proper guides you can change directions a great deal to enable routing the pull-pull lines around structure or to make exit points in a better location.
It just takes a little common sense and a few sketches to set up a reliable pull-pull system that allows you to make the best use of available space for servos, unusual routing of lines etc. If in doubt, connect a dummy setup of what you want on a mockup which is easy to make with some scrap wood, some cardboard and a little time.