I know that new leaf springs will raise it up if your are all played out, but keep in mind you can achieve this look also while increasing the steering and turning performance of your can by lowering the front end of your car by doing a "Shelby Mod". Google it,,,,
Also, some of the mushy-ness in the rear can be attributed to the rubber pads in between the leaf springs and the spring plate that the u-bolts are on.
You can find a direct match to the set up by using Ford Mustang u-bolts, nuts, and leaf spring plates. Cheap mod but you loose the rear end wiggle.
These are on my to-do list for April, the Shelby Mod is supposed to really work well, we will see on my 69'.
Best of luck- J