Hello from WA State.
lowering the rear requires generally new springs, the front can be turned down on the torsion bars, however understand that this is a "cause and effect" situation, every change you make has a residual effect on other things ranging from pinion angle to bottoming out. Not trying to dissuade you from doing this, but you need to understand the effects of it. While it may look very cool, if it is unusable it will not be a fun car to own/drive. You have to remember that these cars were built in a different era than today and were not designed to sit 3" off the pavement. There are a number of things under the car that will not be there for long if you do.
It certainly can be done, my Cuda sits about 4" of so off the ground however I have a 4 link rear end, aftermarket upper control arms and extensive modifications on the overall car to include a road race oil pan, TTI headers, etc. None of this is cheap or overly easy. Probably your best, easiest method is wheel/tire selection.
