The three piece firewalls were a feature of the Briggs and Murray bodies. The removable center firewall section was made necessary by the fact that the fuel tank "cover" was part of the upper cowl and the tank itself was installed under and clamped up against that piece of sheet metal.
This firewall, including cowl and tank was used on the Cabriolet and the various Fordor sedans. An interesting sidebar is that the front door hinges on these bodies are locateded roughly three inches further aft than the coresponding hinges on the Ford built bodies with the pillar post. This allows the front doors to open wider when a sidemount is installed. Gar