When I was building my Kitfox I really started getting freaked out about setting up the rudder cable installation; thinking that small errors in cable length side to side would cause the plane to fly in a skid. Someone on this forum, maybe it was John Pitkin, finally convinced me that it was not that big a deal. In straight and level flight the rudder seeks its own position in the airstream and the only effect of slightly mismatched cables is the pedal position of one foot or the other will be slightly ahead of the other. Your feet cannot feel a small error like that. No real need for turnbuckles to tweak it in unless you are really anal about it. Just set the pedal adjustment at the most forward position; clamp a stick across both pedals to make them even; run the cables around the eyes back at the rudder connection links and clamp them together; then test at full pedal stroke both sides to make sure the pedal clears the FW by about 1/4"; if this is good, clamp the stick back across the pedals in neutral; go to the back and make sure the cables are still clamped tight and the rudder itself is dead centered; if all this is good mark across the clamped cables with a sharpie so you can repeat the same position later after you disconnect the link and the spring tension; then swage the cables permanently. This will get you as close as you need to be.

Later when you start flying, you will probably need to add some rudder trim tab to fly ball centered, which will slightly change your perfectly centered rudder anyway.