ITMike5.0, The lower body accent paint with the thin chrome molding was standard on the Mach1. If the car had been ordered with the optional Boss (Hockey Stick) stripe then the molding would have been replaced with a thin black or argent stripe. That stripe would run the length of the car like the chrome molding did. The body side stripes were a popular add on like the Magnum wheels and would make one think only a dozen were built without the stripes or Magnums.
The rear end squat is typical of the rear leaf spring cars from that area. As these cars aged and the springs became weaker the "Girl Dog Squat" became more noticeable. If not damaged I believe some forum members have had their springs re-arched. Others have purchased replacement springs from the original OE supplier Eaton Detroit Spring. Most of the Mustang parts houses have the one size fits all springs which means that they don't usually fix the problem. Others have installed a half leaf spring which has helped. https://www.eatondetroitspring.com/