Two days ago I finished the installation of the seat, the job was a lot bigger than I expected, but the result is really really awesome, I kan not think of anything better.
Anders dropped by the workshop with an old set of seat springs, great style, but good used. I had to brush the parts with a stealbrush and sandblast everything to get it nice and clean.
I narrowed the setup with 8cm and shortened it 6cm, welded everything up, reshaped the installation bracket and gave it a black paintjob.
To be able to attach the spring bracket to the frame, I had to fabricate two small brackets and weld it to the support tubing at the frame. In the two small brackets I made 5/16" thretted holes, to get an easy installation without nuts.