I was a able to find a very nice used 1968 rear quarter with the indent. The ones with the indent are very hard to find. I would suspect you could find a very servicable used one without the indent. And if you look hard enough you may find one very close to your build date of your car. That would be way more valuable than a NOS replacement. A judge can tell very quickly that you quarter was replaced with a NOS panel.
Not sure if you are going concurs or not.
Rob