Nick,
It is interesting to hear that somebody is has restored one of the Q&TL dump cars. I took a lot of detail measurements of one of the ore car ruins, and started to model it in Solidworks. There is quite a bit of documentation for the design of these cars embodied in the Hartford Products models, but not every last detail. Once the cars completely deteriorate, the exact design details will be lost. As you may know, some of those cars pre-date the 1890 origin of the Q&TL.
There are 3-4 rock cars that were pulled out of relative cover in the boiler house a few years ago. They are in much better condition than any of the others on the site. Here is one truck of the car I measured. Many of the cars have these Washburn type wheels with the cored out axle hubs. They also have those spiral ribs on the backs of the wheels, but I stopped short of that modeling challenge. These are probably 1880-era trucks: