This is what an unrestored dolly mark would look like. Some are circular and some not so much depending on the contact with the mounting points.
2023-09-15_9-13-29 by Marcus Anghel, on Flickr
One thing to mention for those viewing this thread and pictures, the picture above with the double dolly marks is due to the fact that after 67 at some plants Cougars were also built and painted on the same line as the Mustang so the dolly's were modified for two rear mounting points (one for the shorter Mustang and one for the longer Cougar) so you will see two round shadows rather than one which would be correct for 65 Mustangs the focus of this section and thread. What the picture does is show nicely the galvanized surface of the exposed frame rail
Some examples from 65 examples showing the single shadow.
And just so there is not confusion these examples appear to be similar to the later double dolly marks but if you compare them these additional "circles" or "semi-circle" are in front of the dolly hole and produced by installing and removing the dual exhaust rear tie down originally installed on these two cars that use the nut insert in the rear frame section. Yellow arrow identifies the contact damage from the tie downs. On later cars (some plants) the "extra" dolly mark is just barely forward of the rear shackle location.
To round out the collection of pictures in this post here is a shot of a 65 trunk dolly mark while I'm posting