ben;
To go along with the Seat Suspension Kit I offer, I also developed an all-metal Seatback Suspension kit (neither are available currently), but if you haven't committed to the organic rubber bands yet (which will deteriorate again!), you should be able to get much of the important info with which to copy my design, from this:
Chris M. picture used with his kind permission and thanks.
Source:
http://www.sw-em.com/swemkitspix.htm...sion%20upgrade
Cheers