Although it is perhaps difficult to tell from the picture, they do look very similar to the side curtains on my first +4 , which was a 1951 Flat Rad. I no longer have the car, so I can't do any further investigation.
However I don't see any way by which these could be mounted onto the 2 door brackets unless they are on the other side?
The fabric below the window pivoted outwards so you could put your arm out of the car and give hand signals (anyone remember them?)
