Yo! I'm on the road for the next couple days, but if you don't get this before the weekend, please bug me and I'll take some pics and measurements for you.
Hey ebyrd, I took a look at the back of my Crystal Castles and mine doesn't have a vent on the back door. There's a opening on the base between the castors, and the top vent. You can see them in this schematic: http://www.classicarcadecabinets.com/crystal-castles.html and there are some good pics of a disassembled Crystal Castles at the bottom. Now it's entirely possible my back isn't original, but I have no reason to suspect it's not.