James, thank you for the photo links. Those are a BIG help.
I've been trying to imagine how I could modify a coalveyor and seeing that Mr. Baez constructed the top portion from scratch makes it all clear now. The only difference I can see between his models and the prototypes is the ribs that reach the outside of the bottom—he has five "outer" ribs and four "inner" ribs and the prototype has just the opposite. However, if I hadn't been trying to figure out how to chop down a car myself, I would have never noticed that.
Given the excellence of his work, there must be a practical reason he would have done that. For that matter, given the excellence of his work and how crappy the prototypes are, I think Robertson's Ready Mix must be the ones that made the mistake.
I'll have to see if I can find out how to contact Mr. Baez.
— Chuck