Hi, Placing a rigid wire inside of a long plastic tube will almost always result in binding. I usually go with the 2/56 rods that are threaded on one end. they are made by Dubro or Great planes and come in 12 in and 36 in lengths.
If the holes are already drilled in the firewall for plastic tube, then go ahead and glue a short pc (1/2 inch or so) of the tube in the holes. if not just drill the holes slightly larger than the pushrod.
I also drill small holes in the bulkheads where i want the pushrods to travel between the servos and the firewall.
I usually use a z bend on the nose wheel stearing arm. with a heavy duty EZ connector at the servo arm for the stearing.
For the throtle, I use the threaded end with a clevis on the throttle arm and another HD EZ connector at the servo.
usually (1) 36 in rod is enough to make both connections as only the throtle arm uses the threaded end. the left over rod should be enough to set up the stearing. try to keep the rods as straight as possable between the firewall and the bulkheads and at least an inch or so past where the rods pass thru, make your bends near the control horns. and try to bend them to thier attachment points. Check that they slide freely before connecting to the servos. It may take a little trial and error but works well for me. The EZ connectors make for easy final ajustments. Just make sure you tighten them down really well once you set them where you want them, if not they can slip. some guys wont use them for this reason but I have never had one fail in 20 years of building. Sorry about the lengthly reply, Rick