As everyone else has noted during re-assembly, seating the antenna plate is tricky. For me, what ended up working was to attach the hard drive screws first. After this, with just a little wiggling of the plate, the 2 5mm screw holes lined up perfectly.
There may be a small adhesive pad on top of this connector; gently peel it off and save it for re-application during reassembly.
About midway along each edge is a snap. To release each snap, gently slide the flat edge of a Spudger under the lower case, then lift the lower case away.