Having finished off the bottom linkage mount I decided to dry assemble everything to check for any clearance problems, and more importantly to see if my calculations for the positioning of the lower mount were correct. The first problem was that there wasn't sufficient clearance for the bottom of the shock body, so I had to take a cutting wheel to my nice new mount. You can probably just about make out the hole in the picture below.
Having fitted forks and wheels I could then sit on the bike and get a feel for whether the linkage felt 'right'. After dialling in some pre-load on the shock the ride height was about right and then bouncing up and down on the back felt pretty close to a standard bike. The proof will be in the riding but for now I am happy with the positioning.
I am not so happy with the top shock mount.