We find many Pantera chassis that are not perfectly centered in the body, for a whole variety of reasons. Some appear to have been factory-assembled that way. There were at least three different welding jigs used at Vignale Coachbuilders and quite possibly they were not perfect copies of each other. And collisions over the last 45 years- however well repaired- can move panels around a bit. As long as the chassis is set correctly and handling is OK, you can spend thousands of dollars in a frame machine correcting what may well be a cosmetic defect.
But if you continue digging, you may uncover news you will wish you hadn't found: one owner was concerned about differing rear wheel clearances side to side on his car when trying a pair of giant rear tires, and finally found that his beloved Pantera had had a complete replacement rear clip installed....