So it's been over a year since I last posted, and in that time, things have changed. Drastically. I did manage to get the computer installed and working, and I have pictures of the process. However, I'm not going to bother posting those photos because of just how drastically everything has changed.
As I said, I had the computer up and running. It was a very rough install, nowhere near final. It still lacked such components as the GPS, which I was unable to locate a USB adapter for, and I hadn't reinstalled any of the trim pieces except the surround for the screen (necessary in order to route the air conditioning properly). There were, however, a couple of more major problems. The first thing that happened to the amp when I connected it was the fuse blew out. My best guess was there was too much interference from the power cables hidden in the dashboard, since there was a high-pitched shriek that sounded like a load of interference right before it died. So basically, I never had a working audio output. Then, about a week later, the LCD died. I RMA'd it, and I received the repaired one some months ago, but I never bothered to put it in. These two issues plus the lack of a GPS receiver meant that the entire setup was pretty much useless. I really only wanted a CarPC for music, nav and internet, and even before the screen broke the only thing I could use was the internet, which of course I'd have to be pulled over to use. At this point I was quite annoyed, and I decided my setup was overly complex. So I did what any good engineer would do: simplify. I realized my needs weren't that complex, and they certainly weren't anything I needed a full computer to accomplish.
So I bought an iPad.
I pulled everything from my Mac Mini install out of the dashboard, and I sold the Mac Mini to purchase the iPad. As the pictures show, I had severely butchered the case of the Mini, but I was fortunate enough to come across a nonworking Mini on Freecycle that I salvaged a new case from.
Even though I was moving to a simpler, all-in-one solution, I didn't want to settle for a simple mounting bracket. I wanted to actually build a dock into the dashboard. I'm still in the process of doing that, but I've been taking photos along the way, which I'm going to put into a new thread with an appropriate title. So that's the end of this thread. If anybody is doing a similar carputer install and would like to see photos of the semi-finished product, let me know, but otherwise I'm moving on to the improved concept.