I worked at the old Cadillac plant in Detroit for 35 years. We shipped chassis setup just like that to the custom ambulance and hearse builders. The driver sat on a wood crate that contained the instrument panel. Recall that with the former "body on chassis" architecture of automobiles the front fenders, hood and grillage was all considered part of the chassis. The body came from the body builder, in the case of Cadillac that was Fisher Body. At the Detroit Clark Street plant (1922 to 1984) the bodies came from the Fisher Body Fleetwood plant a couple miles away eight to a truck. The plant scheduling system ensured that the correct body got married to it's chassis on the assembly line. Very infrequent that the system went wrong, evident by a car who's fenders and hood did not match the body color.
Joe B