The CN has a few of the small scale test cars, although the ones that look like a "shorty" cylindrical hopper seem to be used in higher frequency. I once saw a short train (possibly a local) on CN that had three different scale test cars on it. It was about 10 cars long and was mostly flatcars. I presume it was to calibrate the scales with the changing weight.

I visited a couple of my favorite search engines (there is more than just Google) and couldn't find any more info. I searched for a full hour, and nothing. But that's expected with the internet. Just because it's not on the net doesn't mean that there isn't more info about that interesting piece of equipment.

I CAN tell you this:
There are at least two more of them out there because it's WDAX #3. If the #1 and #2 are different, then they're probably even more interesting than #3.

Keep us posted...
almo