Looks like you painted your rear wheel wells black. Originally the exterior paint (when the painter was applying exterior paint) passed the spray gun over the opening and painted the fender lip so allot of exterior paint was applied directly to that sound deadener that had been applied earlier. Painters didn't paint the rear wheel wells black over that areas maybe the size of your hand (low outs from the start or finish of a spray pattern) as the pinch welds were blacked out and they came to the front or rear edge of the rear wheel well
As shown in many threads the paint was over the sound deadener (no black paint) and onto the frame rails and more overspray further in towards the center of the car . Originally the sound deadener didn't extend outward to the rear fender lip at the upper surfaces
Rear floor to main floor seam was not sealed also in 67 - or any year at San Jose and most other plants. If you found this originally on your car I would really be interested in seeing pictures of it since it would be the first out of 10's of thousands of examples I've seen through the years
Guess you've seen other "restored" cars shown on the web or in a magazine and assumed they were correct. Blacked out or sound deadener last in the rear wheel wells was a standard detail maybe 15-20 years ago but we've learned allot since from original paint cars so standards and expectations have changed with the knowledge
Noticed also that you didn't do the pinch weld black out either. Going to be more of a challenge to fix these details now that you have started to install parts to the undercarriage
