Movie cars *LINK*

I work in the film industry, and it is common for the "art department" to create spare props and set pieces when there are stunts and special effects involved.
My recollection of the car in the Durango museum is that it was lightly constructed, maybe out of balsa wood, so that it would explode quite well. I think it was to be the spare to the one that did get blown up.
The larger car as mentioned before could have been for horse stunts. When the cameraman lights and frames a shot correctly, most of the audience doesn't know standard from narrow gauge. A lot of the art is in the editing.
I don't know all of the details of these particular cars, so take this for what it's worth.
Dave Schaaf