I first laser cut a bezel for the screen out of some thick black acrylic. I then milled out a recess for the screen in the acrylic bezel. I fixed the acrylic to the mill using this fancy milling fixture I machined a while back.
Rather than trying to desolder the Displayport jack from the LCD controller, I instead just cut and spliced a Displayport cable down to 8". Same with the USB 3 cable. Tip: Splicing Displayport cables is terrible. There's an absurd amount of shielding, along with the ~20 conductors you have to deal with. Avoid if possible.
The thickest part of the entire assembly is connectors. If this project was redone without internal connectors and with custom lower-profile electronics, it could easily be built to iPad-thickness.
For the back panel, I used the side panel of a PowerMac G5 case. The 1/8" thick aluminum sheet is absolute overkill for this application, but I couldn't resist the anodized apple on the back. A more reasonable material may be the back of a broken macbook screen, which would be much thinner and lighter.
I briefly considered just gluing the entire assembly together (it would have been a very Apple thing to do) but then came to my senses and drilled and tapped some holes to screw it together. Eventually I'll get some flat cap screws and countersink them.
To turn the Mini Displayport and USB connector into one piece, I 3D-printed a housing the two connectors press-fit into, at the appropriate spacing for my laptop's ports:
The assembly installed on my laptop: