I know this post is about a 1970 but for those who have 72-74 cars and are wondering how the cable is attched to the floorpan...

The newer cars don't have a clip welded to the floor. They use a white plastic strap... the same strap that's used on the DS inner fender to hold wiring. I assumed that the strap clips into a hole in the small frame to floorpan bracket. In the above pics, there is a brake line clip in that hole. I don't know if the newer cars used a brake line clip at that point or not. That is the only place I can see to mount the strap.