The Panagor has the magnification scale on the rear side of focus ring, while the Vivitar put the scale on its barrel. On the Panagor, it marks PMC (Panagor's Multi-Coated?). The coating colors, green on front element and yellow on rear glass, are lighter on the Panagor. I am not sure, this is because of the PMC or different aging processes between the two lenses.
The Panagor lens shown here has a MD mount while the Vivitar lens owns a M/SR mount and a screw on its aperture ring (in the last image below). A small metal 'leg' might be mounted at the screw site to convert the Vivitar into a MD mount.