The next few pictures will show the evolution of what I hope to be the final solution. The real test will be installing everything in the car but so far it's working out well.
The original idea
I played around with a few ideas and finally settled on what follows.
The New DEsign
A piece of steel square section was cut into a bird mouth so that it could be welded to the main backbone of the engine cradle whilst keeping it horizontal relative to the engine.
Next I cut a hole and welded a round tube to the other end. I actually used a 10mm weldable insert for the tube as the wall thickness was much thicker than any of the steel tube I have.
The threads were drilled out to make a hollow tube for the large M10 Hex bolt to pass through.
Tensioning the chain
I wanted to make a substantially stronger mount point for the rose joints than pieces of drilled flat bar welded to the frame, so I made some custom mounts out of box section.
Spacing between the rose joint and the box section is achieved using nylon washers. The Rose joint can no longer pivot side to side which was the desired effect and can now only pivot up and down.