Assembly Instructions - Page 15, Step 20
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Assembling the upper deck and upper front bulkhead is next.
Step 20
Cut away the upper deck from the #73409 parts tree.
You made need to trim some of the plastic out of the front upper bulkhead screw holes.
Attach the upper bulkhead to the upper deck. Note that the screws come through the bottom of the upper deck, so for instance the picture below is of the underside of the upper deck.
Attach the rear deck. Again, this is the underside of the upper deck.
