I found an internal tensioning device in my Mk2 chaincase.

It looks similar to the chain tensioner for a Royal Enfield Bullet, but that device has a rubber bonded shoe. Perhaps the bracket was shop made to fit a stock tensioner from an older machine.

My guess is that Phil Radford would have an idea on the origin of this. I recall that sometime back in the 70's that there was just such a device offered. Of course my memory being what it is.. oh phooey, I forgot where I was going with this.