I am very familiar with ackerman from my old stock car racing days. But I don't see how ackerman would be necessary on the rudders of a model airplane. My instinct would be to set up the linkage to keep them as parallel as possible (and be very happy if it comes out close!)

I have G-2 but never have tried flying a twin on it. I'll have to take a look this evening to see if I have the Twin-star loaded up and play around with it a bit as you suggest.