proper use of air shocks
think a recurve and heat treatment of the standard springs and a rebuild with pure zinc interleaves is value for money... get the height set where you want it and get the spring hardness/rate set so that it doesn't squat when the boot is full or you tow.
its a brutal process involving a big vice, a torch and a big hammer.. but once the shape is achived and the result heat treated all good. a place that specialises in farm machinery and truck springs is ideal and its never as expensive as you think it will be, they do this all day, and car springs are small cross section in comparison to those off a trailer.
its not exactly precise but i'm yet to find somone who didn't like the result once everythng settled back in
getting the spring pack back together could be a struggle threaded bar and clamps necessary and then some nice cap head high tensile bolts
depends how much you want them to do...
think mine cost £160