Henry Ford wanted the subcontractors to make the new slant windshield cars to the same design for interchangeability of parts and basic uniformity. The Briggs and Murray bodies were pretty much the same in the basic design in each different body model that they produced after that point in time. For example, prior to that, there were a lot of subtle differences between the Fordor bodies produced by Briggs and Murray. The differences were pretty much eliminated in Mid 1931 with the full production of the slant windshield models.
The Ford made bodies had a lot of interchangeability back to day one in late 1927 so he figured the subcontractors should follow that model for the bodies they produced. Ford didn't build any slant windshield design bodies in house at the Rouge or at branch plants. They were all manufactured by Briggs and Murray then sent out. Budd made truck cabs for Ford but they were utilitarian so all of them were pretty plain Jane. The wood bodied station wagon types were all built to the same design as well since Ford supplied all the wood pieces from the plant up at iron mountain, They had one subcontractor for this work in the beginning which was Murray. Later in 1931,another sub was added which was Baker Raulang for station wagon production. Iron Mountain likely built most of the station wagons after they got an assembly line going.