i thought i knew alot about mustangs but i have never heard about an early production cobra rear bumper being different, i saw this car on ebay and the car has a rear bumper like the normal cobras but the whole bumper is cut out from tail pipe to tail pipe, not just a cut out on each side.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7907640775&category=33543
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7907640775&category=33543