My F70 (which is used on road, and across our field) just failed it's MOT due to half a missing leaf, in the offside rear leaf spring.
I got a pair of Milner rear leaf spring kits, which I was a bit wary of fitting, after reading these forums, but I don't think they are as bad as people have suggested. The truck is a bit bouncier (I did tell my bird to wear her sports bra when travelling in it) and about 2 or 3" higher at the rear. I think it probably needs some new dampers as well.
I'm happy enough with it that I'm gonna get new front springs as well (the current ones are curving upwards!).
From my experience, I can recommend the Milner rear leaf spring kits.
1985 Veg oil burning Fourtrak "Rocky".