Pup05 shared his SmartMatrix project in the forum. He writes:
The panel fits perfectly, just had to shim it with a little bit of folded card stock on each side. There’s plenty of room for the Teensy and SmartMatrix board, wiring, SD card, etc. I cut out a piece of white printer paper to size, and placed it between the panel and the glass for a bit of diffusion. The magnetic feet that came with my panel from Adafruit fit perfectly, and keep the panel pushed against the paper and glass. I cut a notch in the bottom of the back, just big enough for the power cord, USB cable, and IR receiver.
I loaded up Craig’s LightAppliance sketch and made a few minor modifications, loaded up my SD card with the animated GIFs I wanted, and everything works great. Unfortunately, I already had my Teensy soldered on to the SmartMatrix board, and didn’t feel like pulling it off to solder the RTC crystal on to the back. I might do that later, and add the temperature sensor.