Here's a few as promised:
https://photos.google.com/album/AF1QipNdxAZTVIHwdrRMTMaHDXuGJ7WkBgo1Esiuiq5P
I also recall the auctioneer saying something about a "factory racing" frame or something. Could just be a sales pitch.
I'm still learning about the whole bike because I've never seen one (I recently looked into one of my old MC books from when I was a kid, and there's no P11 anywhere in the Norton sections)
But the mount looks solid to me.
https://photos.app.goo.gl/j8NSeQPkVwZtTKXf8
I changed the share settings for the album now. Should work. Let me know and I'll try another way. Cheers!
I see 90 degree tabs at the outside bottom to keep this assembly from rotating up, with bike weight, but I don't see yet what is keeping the whole assembly from rotating down.