OK, now I understand what your problem is and it's the very same one we all have with custom set-ups. I'm currently making the bellcrank rod too but am using the dual Carter Webers. Very same problem in snaking through the two manifolds and getting to the lever on the pivit shaft. I bought some 1/4" steel rod and and will thread the ends to accept ball joint connectors. Like you and everyone else it is a matter of trial and error.
I am a little surprised on your choice of material for the heat plate however. It seems to me that the copper tubing will vibrate and cause leakage problems at one end or the other. I've decided on braided stainless hose between the gooseneck and the plate so there will be no worry of leaks or heat burning rubber hose. You may want to consider something like this yourself.
Take a look at my linkage.
http://www.picturetrail.com/birdhtr
