Found it easier to place the SSD in the "lower" position (closer to the bottom of the Mini, but upper while working on the disassembly/reassembly) by resting the Mini on its front side. Easier to move the pegs into the grommets installed in the case. Easier to see if they're not lined up at all.
For reassembly, note that the red T8/2mm hex screw doesn't screw all the way down. It is for the bottom lid to slide-lock onto. Don't look for a hole beneath it on the logic board.