The "leaf link" setup in the DC chassis manual used the SS springs, but an outright ladder bar setup generally uses softer springs... That said, I haven't had much luck finding anything pertinent in my old notes, and just got distracted by browsing through old DC bulletins and catalogs... sorry it took me a bit to get back to you.
What I DID come up with was this:
View attachment 1715516115
which is the formula for ladder bar length that I was talking about.
I stole the image from a good writeup in the H.A.M.B. -it's worth a read.
Technical - Pics of your leaf spring Floaters (fitted)
Hope this helps you out a bit.