Been gone for a couple of days.
Guess you didn't see this when you did your search
http://www.concoursmustang.com/forum/index.php?topic=2824.msg15073#msg15073Since you didn't specify when or where your car was built the following is only a general overview of the subject
There are four different luggage protectors types and locations for you car
1- Rear marker light stud covers/protectors. Looks like 67 talllight studs are similar and could be made to work
2- Taillight mounting stud covers/protectors . NPD had some (listed for a different application) They look similar to the screw protectors (with the small little release from the mold nipple at the end) yet more like rubber than the hard material used for the voltage regulator screw covers for 65-6
3- Taillight screw covers/protectors - These appear to be one and the same as the interior screw covers. Don't know anyone making them currently
4- Interior screw covers/protectors
5- Drivers side wheel house pinch weld strip cover/luggage protector
Two versions - with Calif evap system
And without
Of course if you have a factory rear spoiler/wing there are more