Before a model appears on the hobby dealer’s shelves, there is a long process that leads up to that moment. A decision to manufacture something starts the process, then decisions about just what to manufacture then lead to the design process. Scale drawings are found, the necessary manufacturing tools are obtained and the process begins in earnest.
In the case of the Tenshodo passenger cars, one major decision was to make them shorter than scale length; 62’ versus the accurate 85’. In the long term, this decision would limit the salability of the Tenshodo passenger cars, but it was satisfactory enough to production run of over ten years. And the cars were done well enough to still be collectible many years after manufacture stopped.
It is not known what prototypes these cars were based on, but it certainly appears that many of the cars had a Great Northern Railroad heritage. This would make sense since William Ryan, owner of Pacific Fast Mail (the importer) was a Great Northern fan. The Tenshodo cars all have smooth roofs, which eliminates Budd as a source of prototype; the Budd cars have two distinct roof ridges which run the length of each car.
Regardless of the prototype manufacturer, the Tenshodo cars show respect for producing a car that captures the look and feel of a full length passenger car. If you don’t look too closely, a Tenshodo passenger car consists looks very real indeed.