They're called "quick jacks" or "jack pads". Originally fitted to some 427 S/C's and 289 FIA's as well a few 289's. Someone will correct me if I'm wrong.
On the original cars they were attached to the chassis and were functional jacking points used during pit stops in races. A trolly type thing was inserted under the jack points and the pit crew levered the car off the ground. Apparently they flexed under jacking and caused bends / cracks / stress to the bodywork.
I'm fitting them to my cob (eventually) as I'm going for a 427 S/C look (non functional and purely cosmetic). You can buy them from Finish Line in the US.
www.cobraaccessories.com