The engine in Papa Lima’s photos is not a Gnome-Rhone Jupiter V1 from the Gamecock, But a Finnish built Mercury from a Blenheim. You will see that it has Three bladed wooden props.
I used to be able to 50p balanced upright on my 1964 Triumph Speed Twin on tick over. I lost the whole exhust pipe in the way home once due to vibration.
At last I have been told the magic of getting digital photo’s smaller. Much to the annoyance of my son. I hope this works. Gloster Gamecock, Polikarpov UTI, Hansa-Brandenburg and Folland Gnat with a bit of snow!