WRONG!!! Hope you didn't mount it where he did..Thats an after market valance..I just mounted & test fitted mine today.. if you look at the valance..one side lines up with the edge of the wheel lip & the other side is like an inch in..My after market one does the same thing, I measured both sides & there's a difference of an inch..So If I can't find a good used one, time to extend the short side...I'll take some pics tomorrow & show where the bottom edge of the spoiler should go..but it's not where he shows.
Here is a link to the diagram just click on on it and when you get in just click on the pic again it should supersize. Feel free to browse my photobucket for more 71-73 mustang pics and marti reports etc. hope this helps.
http://i1028.photobucket.com/albums/y349/tomandchelle/scan0001.jpg
Regards Tom
http://s1028.photobucket.com/albums/y349/tomandchelle/
Wrong..diagram is for 69-70..someone penciled in 71-73
Q, If you read the typed print it also says 71-73 similar less the nuts and bolts. It was just a basis to help him out because it shows using the c-clamp as you did and so on. By the way your video was good!