Leaf Spring installation

I've bought new leaf springs, air shocks, shackles all the new items to install the leaf springs. In researching how to do the job what I need to know is I've been told do 1 at a time . My problem the leaf springs on My DUSTER are not A body springs they sit the axle 22" back where the correct leafs sit the axle 20" back so can I still do 1 at a time or should I do this installation in a different way NEED Your help in YAKIMA WA.