On Dec 15, 2019, Jerry LaBant from Liverpool Motorworks.com in Liverpool, PA, USA wrote:
I picked these vintage driving light brackets up from a gent who claimed they came from a BMC rally car. I’m curious if anyone has seen these mounted on any of the BMC prepped cars. These were definitely intended for the Lucas 576 or F700 spotlights as top hole is large enough to accommodate the stalk of these lamps".

Lo and behold, here they are in a vintage picture on one of the 1960 MGA Twin Cam Sebring race cars. (Click for larger pictures).