There a several variations of these that you see from time to time. They use the parts of the O.E.M. set up and effectively move the bars closer to the rider. Some versions might also raise the height of the bars slightly.

Thanks James, I was just wondering what time period they are from and whether they are common or rare.

These are 70's era accessories. They are not what I would call rare, but I doubt that anyone is making them any more. I see some owners looking for a set on IBMWR occasionally. I have a slightly different set in one of my parts boxes. The effect there is that the additional rise is mostly offset by the rake of the frame geometry where the top plate is angled away from vertical. As your picture shows, the device(s) put the handle bar to the rear of the damper handle as opposed to in front of it, which is where it would be normally. This creates an interference when trying to remove the fuel tank.