Im not even getting into this. You are overthinking things. The bodies are all the same in the econline series. It is not a unibody, but a body on a full frame, all the same frame rails. I can provide part numbers, if needed to prove this. Do you know how costly it would be for the manufacturer to have different frames and bodies for a 150, 250, and 350? I shared the above post with my friend at Ford and he is still laughing...suspension, cooling, brakes, rear ends, etc are all different.
In talking with my friend at Ford, let it be known that I was incorrect in stating that the 3 valve per cylinder version of a 5.4 engine cane in the econline series van. That was wrong, as only the 2 valve version of the 5.4 engine was installed at the factory in all econline gas equipped vans. There were some that came with a v6 engine, but not many.