Well, it's all back together now. In case anyone was wondering about how I wired it up:
Cover fits on ok, I think it touches the wires, but that suits me as it will stop them from falling out. I did it this way so any service I get done can have the module removed - as it will be requesting data every half second. I've marked the plug with a sharpie pen (lighter colour wire - white, which is just showing - goes into the H pin).
For 12v power, I just soldered a couple of wires on to a 6 pin Arduino header plug and used my previous "flappy paddle" mod connector. This is sort of neat, as it's easy to unplug all this stuff (can't think why I'd want to though). That is also the battery saver power, which turns off after 15 minutes. It's all been working pretty well too - turns on and off exactly when needed and the gps/nav stuff doesn't notice any problems.
I did have to remove my high-priority setting for drawing the gauges (to prevent flicker) because I noticed tiny breaks in the audio when playing mp3s off a USB stick. No big deal, it only seems to flicker when I change the volume. Most of the time that area of the screen doesn't get re-drawn so it's all good. I've attached another zip (just rename it). There's vague instructions on installing it on the nav units in there, and a couple of startup.sh files from my two units that I've already applied the changes to. Use the one that matches most closely what you have, I guess.
The gauges also display when you're in reverse and the camera turns on - I was wondering if that was going to work. I thought it might because they showed ok when I entered the nav software on the work-bench.