Goldberg Super chipmunk dual servos
Any time I do surgery to balsa sheeting, I always try to go across at least two ribs, and at least 3/4" past the ribs. Don't worry about cutting through the ribs, just peal the sheeting off of them, whatever cracks will be re-glued later to it's mating part.
Once the internal repair is complete, glue tabs made from balsa sheeting UNDER the sheeting around the opening. Now the piece you cut out will have a "bed" to rest on that will line it up with it's original position. Then just fill the cut lines with balsa filler.