Phil,

if you need a wider stance, may I recommend that you leave the original ribs in their position and make two sub-ribs (only D-tube section) to hold the retract body. Cut them in balsa and then use those as a template for the 1/16" ply doublers. The interfering rib in between where the body might go can be relieved to suit. It's good to have at least half a rib (the top part) in the D-tube section near the root.

What retracts are you using? What about servos?

David.