The first stage of assembly after the frame is the pulley set for the Z stepper in each corner of the printer (four Z motors, and belt-reduction, and belt attachment to the gantry). The instructions call for the 625 bearings and the GT2 20T pulleys … so which of these unlabeled bags would those be?
Well, I can rule out the bags with two and three parts, since this needs four. I can rule out the spool-shaped pulleys since that’s not what’s shown in the instructions. That leaves two sizes of pulleys and it must be the larger, as a nearby assembly step calls for the 18T pulleys, which one expects to be smaller than 20T pulleys. And from the published dimensions of 625 bearings, they must be the larger, whose size relative to the 20T pulley does match the assembly diagram.
The shaft is longer than the stack of pulleys, bearings, and shims, so where to position the pulleys within the stack slack? I opted for squished to center as tightly against the shims as possible; and this works out to have been a good choice, as the black 80T gear comes very close to the edge of the recess on this part and its mate, so moving it toward center and keeping it from sliding around are important.