No significant difference as long as they are both slant windows. The vertical window sedan of early 1931 had the same amount of wood as the earlier bodies.
Slant window Fordors made by Briggs and Murray have interchangeable body parts. That's what H. Ford demanded of them! The fit of the firewalls fit into the cowls are the same for both 1931 straight & slant window cars.
Many of the early sw's had the support for the steering column attached at the gas tank with the straight firewall, then later moved to the dash rail (see the Service Bulletins, etc.)