Also search for some posts about using aluminum drop-ceiling supports. They are about 1.25" wide (guess), "L" shaped, and sell for like $4 in 10 or 12-foot lengths at Home Depot. Hack-saw and black paint and you are in business. Several people here have had success this way.
I just spent some time in an arcade looking at marquee brackets on different machines and several used similar arrangements (often times with a Happs bracket on the top and an aluminum "L" on the bottom).
My marquee lexan is recessed by 1" and currently held in by friction. I'm still brainstorming on a permanent home-brew solution but intend to try a variant of the "L" brackets I just mentioned.
- pmc