Robin, this car may not be related at all to your inquiry, but I thought I'd post it, this is from my files, noted as "partida de las seis horas, peruanas (Peru) ? 1966. We see a Cobra #3, two, what could be GT350s, #s 6 & 7, and what looks to be another Mustang, two spots behind #7.
I don't know how they qualified for this event ? but it looks as if an Austin Healey, and a Lotus Super 7 were faster then the Cobra.
Mike