Ismael: That's a good idea, but it's also a good idea to back up the SSD before beginning the Macbook disassembly procedure. This way you'll have two copies of your data, and you can plug the backup into another Mac if you need access to it before you've got your Macbook reassembled, especially if something goes wrong during reassembly that prevents you from using your Macbook for a while.

maksoft121: Replacement used logic boards can be bought from iFixit and also from eBay, many at reasonable prices, but make sure they come with a warranty of at least 90 days, and be very certain to doublecheck the specifications of the logic board you need (appropriate model, speed, amount of RAM, single (integrated) or dual (integrated plus discrete/external) GPU; etc.

justinlyon: Different placement of some parts on the logic board is normal with different logic board speeds, and differences between the Late 2013 and Mid 2014 logic boards.

Marcel: The 3.9mm screw threads into a metal standoff (not a nut) that's glued to the logic board. If this standoff comes off of the board, a drop of superglue may allow it to stay in place, but to position the standoff properly while re-gluing it, first reattach it to the fan with its screw, then place a drop of superglue on the bottom end of the standoff, then drop the fan back into place and apply a little pressure to the top of the screw to help the superglue stick to the logic board.

To answer Keir's request for more detailed photos of the routing for the cables near the lower left and right corners of the display: click on the photo of the display in this step, which will open a higher-resolution version of the photo in a new tab, where you can click on this photo to magnify it so you can see the cable routing in the corners in larger detail.

wkurosawa: The optical drive will stay put properly if the screw on the left isn't installed.

Edward: Philips 000

Good point. No, the Non-Energy Star and Energy Star cables aren’t interchangeable, due to the different pinout you describe.

DaR: this is usually a 2.5mm hex screw

Glenn: you might get some extra speed from those SATA drives if you install a SATA card into one of the PCI slots (if you can still find one), and connect the drives to it. I ran a couple SATA drives in my MDD this way for years, before the MDD’s power supply burned out.