Probably easier to scratchbuild, though...the Ranchero-specific parts (roof, bed, rear quarters,taillgate) of the '72 look nothing like the '70-71. The '70/71 and '72-76 Torinos and Rancheros have no panels in common, I think..
One of the resin casters (it may have been Mini Exotics) did make a '70-71 Ranchero back around 2000, probably hard to find now...