Ok well here is an update. Instead of going with my original idea to trim the lilliput bezel and put the plastic dash trim over it, I decided to just make the lilliput bezel narrower horizontally. Vertically, it is actually perfectly sized for my double din. So all I had to do was cut out a 1cm vertical strip, mash the two together with epoxy, then bondo up the holes.
So far, the actual fabrication was easy. Even sanding the bezel was fairly straightforward. But for the painting, I had to scrap it and resand twice because of minor imperfections. The can sure wasnt kidding when it said to apply it in small coats. Mostly I have been having minor mess ups with the paint over the bondo'ed and epoxied areas. But so far my last attempt at painting is looking good, so hopefully it will stay that way. Just a few more coats and Ill be ready to stick it all together.
Oh wow, the paint has finally done drying and it looks awesome. But to be honest, I kind of wish I went with a flatter black. I dont know how this gloss is going to hold up or whether it will match the car as well. But Ive designed everything to be taken apart, so I could repaint it, or upgrade to a different 7" monitor if I wanted to. Otherwise, I am very happy with the results.