Those pictures are of a day cab. I think it sounds like you're wondering if you bought a tractor with a sleeper cab could you build a truck conversion out of it and put a large bed above the cab of the truck? If it's a low or mid rise sleeper cab I would think you could build the conversion with an overhang above that and put a bed up there. If it's a tall sleeper then you wouldn't be able to because it would be too high I think. Basically all of the bed overhangs I've seen have no contact with the cab portion of the truck. They're frame is a part of the conversion frame. Am I understanding the original question right now?
'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio