I decided to build the left flap first and then the right. Since the parts are the same but a mirror image of each other, it made sense to separate all of the flap parts for each side and not try a parallel build. It just seems too easy to mix these parts together incorrectly.
I pulled all of the flap parts off the shelf and carefully read the plans to figure out the exact parts for the LHS. The LH flap parts were batched together and the RH parts returned to the shelf. I spent some additional time on the skins marking them for upper/lower surface, IB/OB and fwd/aft. Hopefully, this time spent will reduce or eliminate any confusion moving forward.
Drilled one of the FL-1007-L brackets and used it to match drill all of the other (RH flap parts too and put them back on the shelf). Deburred the nose ribs and doublers for the hinge rib and rod end rib subassemblies.
Started on trimming the small tab on the FL-1005 ribs, but only completed three of the eight before my back told me in no uncertain terms that I was done for the day.