Some states did not like the gas shut off valve being located inside the cars. I heard one of the states was Pennsylvania. The indented firewall was to relocate the gas shut off valve. The sediment valve was then moved from the firewall to the carburetor.
Dave
Dave, this is probably what you meant, but wasn't the reason why for the change actually because a fuel line could not pass thru the passenger compartment? Most racing sanctioning bodies still have that rule, and so many (-including NASCAR) circumvent this by placing the gas line inside of a larger piece of steel tubing.
To the original poster's question and reply, I would want to go pull the prints and the ERs (Engineering Releases) to confirm this first but let's consider this theory for the immediate time.
While we do see some glass sediment bowls incorrectly used, those that are used are/were not Ford-manufactured ones. While the zinc based glass bowl types were tried for a few months of production in 1929, it was chosen to go back to the cast iron sediment bulb due to costs. Additionally I would expect liability and rigidity are the major reason for Ford's side-bowl design as we know it. From a safety's perspective, there needed to be a shut-off valve at the exit of the tank (-in which there was), and if a sediment bulb was placed after that valve, you are potentially creating a rigidity issue as well as a repeated safety issue with a drain valve located overhead of an exhaust manifold. In the manner the engineers designed the side-bowl carburetor, you had a much simpler and smaller unit to cast with two spotfacing operations instead of the more complex threading operation, and it used a smaller length of fuel line. The core of the carburetor was easy to modify to cast the fuel entry port in a different location, so it really was not a difficult design decision from my perspective.
One other point to understand is that Henry (-who had very little input on these type decisions by this time) was NOT cheap as you are inferring. He had the same mindset of any businessman in that the company was constantly seeking ways & methods for saving money. As for saving the Agencies' (- his term for dealers) money, ...their inventory was something he did not own. In addition, there were plenty of aftermarket carburetor manufacturers that were competing against him, so with a new design, he had the market cornered for a period of time.