The Behemoth won't reply? I'd go the DIY route like i'm sure they did and blaze your own trail to the finished product. From what I understand it was two displays put together ala 6-player X-Men, maybe start by looking up the dimensions for that cab and adjust to your own needs accordingly. Figure out the following:
-CRT or LCD?
-Will it fit through the doors it needs to be able to fit through to get where it's going when done?
-If unable to fit when assembled, is there any way your friend could build it in such a way that it can be disassembled for transport and (relatively) easily be put back together?
I'd then try and secure two identical (or as close to identical for your budget) displays and use the "build around your monitor" rule of thumb that comes with arcade building.