Same box as my F1 and a pain until you get it. The box has, as you say, two long bolts from the top that pass through the top half and then are held in by two small threaded spacers. The bottom half has two larger bolts that are actually sleeves threaded inside that thread into the upper half bolts. The threadded spacers are there to hold the top half together, but should unscrew easily from the bolts on the top half, allowing you to get the whole airbox apart for cleaning or whatever.