As I've mentioned in my diatribe elsewhere. The operator had no input in the design of the first 7 cars (the ones with the flat roofs.
When the second series of cars were proposed, we had some severe economic and practical issues to deal with. First of all, as mentioned above, as traditional narrow gauge passenger coach as real crummy visibility. The seats are real narrow. Seating was a real issue, as obtaining/creating walkover seats for narrow gauge cars was very cost prohibitive. We found a treasure trove of walkover seats removed from Lackawanna commuter cars that were being sold and scrapped. Be literally bought multiple truckloads of seats. The width of the cars was determined by the seats. The seats make the cars about foot wider than a typical narrow gauge car.
The basic profile was based on taking a drawing of a narrow gauge car, and drawing of a 6500 class flat car (which is what they were built on) and with some creative "scissors drafting" came up with the basic concept. We solved the visibility problem by making the windows wider and having the window in a single sash that dropped down below the belt rail creating a nice big window, that you can stand up in front of, lean out and take a picture (or get whacked by a tree branch if you're not looking ahead). Using fiberglass siding eased construction and maintenance.
Late versions got fancier with rounded corners better railings and so forth. The later cars were built on frames from cut down 40' standard gauge box cars.
If you build a car from the ground up, you have to deal with certifying it's strength and crash worthiness. We were taken to task by an FRA inspector when we built the cars. When we explained the cars were built using existing center sills, bolsters and draft gear, they left us alone.
