Hi all,
I'm doing this upgrade, and just FWIW, my Spin 3 had the M.2 riser for the screw installed. I saw some early posts talking about acquiring hardware, and brackets, but mine had the riser. I just needed an M2 screw. NOTE: that's METRIC-2, not M-dot-2 
I got an M2x5mm pan-head screw at Home Depot which worked. BUT, I advise getting an actual screw meant for this purpose because the head of the screw is not quite big enough to make good contact on the drive.
Here is a shot of my machine after I opened it up and placed the M.2 drive, note the riser was already present, not something I had to acquire.
And here installed with the M2x5mm screw. You should use a washer or a proper M.2 screw:
And wider view, installed:
