Take a look at this factory photo, that mat is under the firewall cover.
http://www.flickr.com/photos/advance-design_parts_co/8295962190/in/set-72157632304126997
http://www.flickr.com/photos/advance-design_parts_co/8326841304/in/set-72157632386552074
On the windlace retainers I don't believe the mat goes under there. I would base this on the fact these were work trucks not hobby vehicles and it would make no sense to remove these for access. I would also base this on the fact that removing a set of those for the first time during restoration those screws have been here since day one.
