the leaf only has to hold the car at the desired hgt.
Once caltracs are installed they controll axle windup.
Do you have local access to a spring manufacturer?
someone make truck springs/repair?
I think I still have print laying around.
or just use a set of good 4 leaf slant six dart springs. think they are symetrical.
If you have a spring pile you could take the leafs apart and make you own set as long as they are the same dimensions.
Use a heavy main leaf and a few smaller ones to suite your ride hgt desires.