The devil is in the detail, they say. Casting around for small jobs, I realised that I had nowhere to mount the brake light switch. I knew from studying the wiring diagrams that Ariel began fitting brake lights to Square Fours around 1953, so that early Mk 2s would have factory fitted switches.
A plea on the AOMCC forum yielded this picture, from Greg Snyder in Pennsylvania, USA:
Greg also posted this, of the bracket in situ on his bike:
So, with guidance like that it was easy to make a new one: