Rick & Darryl - if I were spec’ing a KW for this application it would leave the factory as a “tractor” meaning rear lights and mud flaps installed, trailer air and electric installed, 5th wheel installed or frame drilling done and a tractor braking system, with a “customer/body builder installed sleeper or dromedary box” option. It would be a “complete vehicle” (ready to couple to a semi trailer with no further modifications as it leaves the factory), without any “incomplete vehicle” documentation. The tractor is compliant as is and the customer could actually register and plate it as is without the sleeper. The big sleeper company is responsible to provide compliant lights and reflectors etc. KW would request info regarding the weight and dimensions of the “drom box”.
A “truck” is “incomplete” - a cab and chassis meant to be further up fitted with a cargo or equipment body and may or may not have trailer air and electric. It could receive hitch or fifth wheel. It has a different braking system. It cannot be registered and plated in the form it leaves the truck factory. It becomes a complete vehicle after the body builder installs the body and/or equipment. The body builder is responsible for final compliance such as c of g, hitch location, box length (over hang), braking standards etc.
Engineering drawings and info would be sent back and forth and reviewed by KW to ensure c of g above the waterline is good, frame strength is correct, steer axle brakes are correct etc. before the spec is priced and ordered.
Taking a tractor and lopping off an axle and changing the wheelbase and adding high loads behind the cab and placing a heavy pin load from a semi trailer (even a 12 ton rv trailer) many feet behind the drive axle etc should be reviewed by the truck oem and / or a body builder engineer before work commences to ensure component loading, braking and emergency situation handling and stability remain inside safe parameters.