A friend e-mailed this website, a large collection of photos of airplane prototypes.
http://rareaircraf1.greyfalcon.us/UNITED%20STATES.htmThe e-mail came with a note about the Conestoga - believe it or not, one was made into a gas station in Ft. Worth.

I was intrigued by the 3rd set of photos from the beginning, the ARUP S-4, with "Sears & Roebuck" all over it.