Stew,
The basic trailing truck is the same on the Hudsons as well as the Notherns. But the one on the right with the upright is only used on certain Northern's (I think). The two I have don't have the upright, but I've seen them elsewhere, but I can't remember exactly on which ones. Then, it could also be an add-on by a tinkerer. Is it spot welded, or somehow else affixed?