I made a cardboard cutout of a 20"x20" square. I then printed my letter matrix to scale (6 sheets of 8.5" x 11"), combined with tape, and trimmed to fit. I then drilled a hole at each letter in the matrix (256) in a rough location. The hole is sized slightly smaller than the LED's I plan on using to allow for a snug fit. I was planning on wiring up the matrix last night, but had a few other things pop up. Here are a few pictures of the cardboard cutout and letter matrix (with and without holes). There is also a picture of the cutout in the shadow box I'm using for the container.