[David_Hayward (RIP)]

I suggest that the General Motors Truck was a Thornton conversion [Thornton Tandem Axle Corporation, Detroit]. Leyland had a subsidiary or agency in Leyland Motors Ltd [of Toronto I think], but the Thornycroft is a new one on me!

These trials are very similar to the 1930s ones by the War Departrment: see VINTAGE ROADSCENE magazine. I have written on the 1936-7 Trials and the next issue in the series has photos of 1935-7 Trials, recently found.