I don't think you could accurate guage the required spring rate when using leaf and coilovers together.
The amount of fab work required for towers and re-inforcing the rear chassis to handle the 4 link (or 2 link) setup would be almost equal to a proper ladder bar setup, then everything is off the shelf (albeit a shelf made from GOLD)
Then you have lateral forces youd need to support aswell. Panhard rod or watts links setup
Some ideas
http://www.rodandcus...ng/viewall.html