Never understood how pre 1960 bike races droped bump starts. They were a great spectical and a theater lost. The silence on the line the shuffling of boots as you tried to get a good footing the worry in my case if you had got it back on the rear cylinders compression. The scattered starting of the engines building into a roar as the grid got away.
I saw Mr Dunlop take the recreation of McIntyre 100 mph lap at least he tried to bump start ungainly straddle that it was. but watch Mr Hailwood
poetry in motion, a few powerfull steps, clutch drops in concert with maximum weight on back wheel, note how he guns it side saddle left foot already on left footrest then lifts over and right foot comes down to footrest and change to second all in one motion ..magic