i have 70 duster with 318 also,stock rally wheels i did replace rear springs and hardware through espo but went with 1" lift added.it sits just about perfect but probably has 2-3 inches above rear tire when sitting.Double check everything as it appears to me your car is sitting crazy high.check tire measurement as lower tires may be a change that improves ride.I do think if you have years since spring work rearched do flatten out again.Talk to laura at espo she was great