First of all the original plans are not going to be good for much more than the outlines and cross sections. Assuming you're going to want to sheet the model to act as a base for a shiny finish to simulate the typical polished finish on Electras you'll need to plan on sheeting the whole model. Also you'll need a far more adequitely designed wing spar, provisions for removing the wing yet retaining the fairing, etc, etc. The linkage at the tail will only be one detail and by that time you'll probably be able to figure it out.

But basically you need a pushrod to a multiarmed bellcrank in the tail or mount the servo back there and run 3 pushrods from the bellcrank to the tail wheel and rudders. Depending on how it works out you may be able to lock the bellcrank to a vertical rod that is also the axle for the tail wheel so you kill two birds with one bellcrank.