Rear subframe brackets...

[Ross]

I think the PO may have had this made to take either some form of saddle bags or a trailer hitch attachment point.

I would agree with that idea. Thing is, I would have expected to see a hole or a threaded stud for either purpose. I wonder if it could be for a seat rest? If so, then the legs of the seat rest could go through the space made by the brackets and either have a lip or a keeper of some sort to keep it from coming off if there is any weight on it.

Chuey

Now that could be it too. I was wondering about the lack of holes in the brackets.