Teo,

if I may comment... that is unnecessary on a model this size. A simple doweled 1/8" ply plate embedded into the surface of the core is all that is needed. You can see how I installed light mechanical retracts into a 40" span wing in this thread:

http://www.rcuniverse.com/forum/m_8196707/tm.htm

I'd say that the E-Flite gear while very nice is a little too large for classic models in the 40" span. It is better suited to models in the 3 to 4.5 lb range. Don's excellent mini pattern ships will probably weigh less than 2 lbs all up.

David.