Thanks for the photo of Surtees(?) hanging off the Vincent. I will pass it to my Pommie mate who was a childhood friend of his.
I have some old movie of the guys racing at Winton back in the 60s when I rode regularly there. The bikes are going around the corners almost vertical. I used to hang off the bike because of the bad tyres. In the 70s, many of the guys had gum-ball tyres, and the angles of lean increased dramatically. Most of the 60s bikes had neutral steering, however the Manx was slightly self-steering. When you rode it, if you got in the shit it always felt better if you drove it a bit harder. When you compare those old bikes with moderns, it is chalk and cheese. Bike handling is not a continuum. You choose which way you want to go. If the bike has skinny tyres and the handling causes it to tighten it's line in corners, it will go around more vertical. Modern bikes cannot be set up to handle like that because of the much greater power they have. The quickest way around a corner is not necessarily maximum lean, big sticky tyres and stable handling. The only real advantage modern bikes have is in a straight line. When I practice, they are always there and I usually out ride them in tight corners.