Cliff:
Those vans were used as shop vans, commo shacks, command vehicles, admin vans, etc, as you know. The basic layout would vary by use -- for example a machine shop van would be different than a small-arms repair van ... and so on. Also most units would then chnage it to suit their purposes -- especially the office, admin, command vans. In short, once you have an idea of tables, shelves, etc, you can pretty much do as you wish (IMHO).
Anyway, you might try Portrayal Press -
www.portrayal.com. They don't list much on their site so getting a catalog is helpful. I found ORD 9 G-227 "Bodies, Shop Trucks, ST-5 & ST-6 List of all parts & equipment" 128pg.
You might use the site to send email to Dennis Spence, the owner, and ask specific question. They have a lot of un-listed manuals & will do a special run, but they do cost some big bucks.
Of course, this is all, "US" info ....
John