On yesterday’s ride I was looking down at the rear brake when I had a giant light bulb go on over my head.
Why not just use the rack mount just out of view at the top of the picture? On many bikes as with this Rambler, the light interferes with the chain stay and can not be properly aligned without a spacer. Often in my experience the spacer will end up letting the bolt come loose. This coupler solution solves both the mounting of the brake pad and the light with a single commonly available piece of hardware. I have had the Superflash down at the rear drop out for a few months now, but find that I am more likely to turn it on if it is up higher.
Hooray for the corner hardware store that stocks plenty of bike friendly Metric nuts and bolts!