I would add three toothpicks or bamboo "skewer" dowels into the repair to give rigidity to the stab. The epoxy alone will probably work, but you've split all the grain that gives the balsa strength and toothpicks will add immensely to the strength. Put a round head pin on the seam, align the pieces and press down hard. The pin head leaves a mark on both halves that you can then use as index marks to drill into the wood. Once ypu have it dry fit well spread on the epoxy with a paper match spreader and put Scotch (transparent) tape over the seam overnight. The tape will peel off leaving a smooth and shiny seam. If you're careful it can be done pretty near undetectably. Well, almost.