Tony Brooks, organiser of the Torbay Steam Fair and who originally thought up the idea of recreating feat of engines climbing the hill to the green where the fair was held was telling me about a photograph that exists of engines tackling the incline during their working days. I'm not sure if this is the one he was speaking of but I've managed to find this one of Anderton & Rowlands Lord Nelson taking trucks to the Brixham Regatta in 1928:
Lord Nelson is pictured from the other side of the road exactly where Princess Marina is in cocky_1987's pic here:
