Well the answer is rather long & somewhat complex. if you are looking to use the 4x4 married box spicer that came in many of the AMT kits such as the Diamond Reo, Western Star or Road Boss, then both sticks would be fairly close together in the cab & that transmission can be detailed up quite nice.
If you are looking to use a 5 & 4, then the 2 transmissions from the AMT KW W-900 / Alaskan Hauler . Challenge mixer & the T-600 is what to use. All of these kits share the same chassis & drive line (of which as we know is totally wrong for the T-600). For that installation, the 5 speed main box is mounted to the engine & the 4 speed auxiliary box is mounted about 2 to 3 scale feet behind the main. Linkages are separate to each transmission. I will look in my files and see what i can post for images of each set up.