I hope you don't mind me jumping on this thread...
My cabinet has an odd shaped marquee.
It's exactly 24 inches long and about 30% taller than a standard marquee. However, the bottom third or so is covered by the metal speaker "grille" area that wraps around from underneath.
The bottom is held in by the aforementioned "grille", the top is held in by a plastic piece that is like a rounded corner and is held on with 3 screws into the top of the cabinet.
I'm not really happy with the nonstandard marquee size but what can you do. I'm sure when I get my own custom graphics up there that are sized and proportioned properly, it will probably look good. I'm even thinking about cutting back some of the grille to expose more marquee glass. If it's gonna be non-standard, maybe it should be REALLY non-standard.

