If I remember my discussion with Vans last year correctly if you buy the QB fuselage first you have to also buy the matched wing main spar also which Vans will store until you order the QB wings, they will then credit the cost of the spar against the price of the QB wings. If you buy the QB wings first I assume you get the matched center section that you have to return to Vans for installation in the QB fuselage (this is what I plan to do although I went for slow build wings with QB tanks)
Best advice to check for sure is call Vans, I found them very helpfull.