Reminds me of the time I scratchbuilt a single-unit clone of a K-Line spine car to carry a "Toy Fair" container.
Previous Toy Fair freebies (for their collector's club members who came to the showroom) were rolling stock, so I sought to continue the streak by building a car to carry the container. I simply took one of the K-line cars, a scale ruler and some styrene and went at it till I had something. My workmanship is a bit crude compared to yours though
---PCJ