It is suspected that the boxcar started life as simply that, an experimental boxcar. The NCNG begin constructing freight cars far earlier than traditionally understood. I did a quick check through state reports to the railroad commissioner and found the following freight car totals.
1876 - 15 8 wheel platform (flat) cars, 15 boxcars
1877 - 20 8 wheel platform cars, 15 boxcars
1880 - 20 8 wheel platform cars, 18 boxcars
One of the reasons the car looks like a flatcar with a body is likely because such a process was not uncommon, this would make the car a boxcar regardless of being a flatcar with a box frame. As we can see from the car totals, the need arose for more flats, however the total doesn't change. Is it possible that the shops were building flats and converted one to a rudamentary boxcar? Indeed. It is important to note that between the end of 1877 and the end of 1880 the shops built 3 boxcars. Since these cars are NCNG knock-offs of Carter designs they're 26' long rather than 24' foot. There is debate of course as to the flats being 25' 4" initially, or if the 5 cars built between 76 - 77 were of this length. So lets assume boxcar 32 is constructed from some sort of flatcar frame, the frame design would match the other flat cars the NCNG had been constructing, which we can assume were 25' 4". By taking this basic frame layout with a home brewed body on the car, then applying siding, you get a car that is roughly 26'. It is a documented fact that car 32 was 26' long by the end of its life. There are differences between what you're seeing in that photo and the Carter cars themselves. The frame on that boxcar is wider that the flats following it, there is also a lack of stake pockets on the car, or indications of there being stake pockets. This would indicate the car was constructed for this purpose, if it is 32, we're looking at the foundation of the cars the GV shops would continue to build for many years following. A common flaw with boxcars of similar design is the exposed bracing and simple wall design. The V&T had issues with their outside braced cars and later rebuilt them with exterior siding. The NCNG would have endured the same experiences leading them to convert any boxcars of this design to a more traditional design, this of course would be the 26' GV shop built cars we all know and love.
For the record, the extent of the "Kit" form for the first cars is under debate. I have documentation that one of the Carters WAS in Colfax and Grass Valley and was in charge of several pieces of equipment. Among those is the Grass Valley turntable. In coming months after I sort out my notes and research, I will be re-writing the earliest history of the NCNG. I had been keeping a lot of this under my hat until I was ready to announce it, stay tuned.