Lots of options

1. Keep the leaf springs, move them inboard, install some housing floaters and ladder bars.

2. Trash the leaf spring, go to a coilover setup, then you have the choices of a 4 bar , triangulated 4 bar, or ladder bars. Then of course with any coilover set up you'll need a device to control lateral movement of the rear end, this can be with a Watt's linkage (best), panhard bar (acceptable) or a track bar (drag strip use only).....

Lots of room underneath for any of the above setups..... Everything accept the stock leaf springs will require a new back half for the Ranchero, though, as it's a unibody and not a full framed car... Or did you already do a new frame????