 Another subtle difference between the 'open' back models Vs. 'closed' back models was the method of body attachment to the chassis.On 'open' back models the rear chassis outriggers were designed to accept customers' own coachwork either attached via welded cleats or bolted directly.This bodywork be it a pickup buck or say an ambulance body typically added extra stability to the rear chassis however should not be considered essential because the chassis design is constructed so as to be sturdy enough without.