I cut open these rudder cable slots. They are sliced-off plastic tube guides, covered by Ultracote. It didn't take long to find them if you just poke w/ fingernail to see which region would give.

Oh, I plan to use higher-strength pull pull cable, but use the same end-point hardware. The provided cable feels like a guitar string, somewhat flexible axially. I had the same cable in Super Stunt 60, and the rudder would move due to flexing of the cables themselves. This may be good to save servo, but not sure if it's the best for 3D.