Just after the post yesterday, I found out what the parts 39 & 40 are for. They are for the battery packs.
The clue came from an opening in the front part of the wings through which the batter packs can be swapped. The original suggestion is to use a NiCd 3000mAh. Which will have to be replaced by some suitable LiPo. Which means that motor and battery packs should be chosen first to confirm that they will fit the allotted space.
Fixing the location of the battery packs before the build is finished means that it is no longer possible to correct the COG (Center Of Gravity) by moving the battery location. And since some changes will be made to the construction, … hmm, have to mull that over a bit.
Btw: The placing of the battery bays is a logical one, it allows the shortest possible leads to the ESC/engine. In the article at Ivan’s site (see first post) he does mention that the leads between battery and ESC must be as short as possible to prevent induction damage to the ESC. The perfect place for the ESC would be below the motor. That way it would receive cooling air from the lower opening in the front of the nacelle’s. But that also places it quite some distance from the batteries. Probably making it necessary to install some capacitors as well to prevent the induction damage.