Wow, that Metra kit looks like crap. Especially the buttons. The screen is pretty cheap looking, too. I think you guys just need to find a reputable stereo shop around you that builds fiberglass enclosures for subwoofers and stuff. Any good shop should be able to build you a custom dash panel to hold a double DIN head unit. They should be able to use the stock panel, cut it out, and use fiberglass/resin to fill in what they need.
You would likely have to paint it. If it's hard to match the finish to the stock panels, just have it all painted another color. If you look at the new Saleens, they have all the trim painted gloss black. It looks badass.
I wanted the Shaker 1000 system, but I'm so glad I got the Electronics Package instead. The nav system/screen is one of my favorite parts of my car.
2011 Mustang GT - Kona Blue, 6MT, Brembos, 3.73s, Everything but auto & glass roof.
BMR Springs, K&N Drop-in, Magnaflow Street Axle-backs.