Nice install. I just got my Lilliput installed in the factory stereo location and moved my HU down to the lower pocket above the cup holder. Hardest part so far was getting the screen in the dash right. I ended up cutting the buttons off of the front bezel of the lilliput and rejoining the bottom of the bezel - can't even tell it was ever there.
Now I'm stuck trying to find out where to mount the PC. I would love to have access to CNC equipment, because what you did seems to be ideal. If you would be interested in fab'ing one up for me, shoot me a pm. I've been leaning towards installing under the middle back seat, but I would rather not. It would have to be pretty low profile for the seat to fold down properly.
BTW, My truck is a 04' Sierra 2500HD CC, everything is exactly the same as your truck. Nice job - looking forward to hearing back from you!