The balsa sheeting was to add stiffness. Also, it could serve as a base for the truss member. A long unsupported stringer (truss link) will be prone to buckling, the balsa sheeting will prevent that. Plus it will prevent the link from seperating at the ends by giving more area for adhesion. So let me see what can be done

I want to keep the engine 20cc, lets see what happens. A temporary install using cable ties to check the balance is in order after I finish the remaining assembly

Ameyam