Mike,
There are two different style brackets. The long brackets that attach to the top and bottom of the rear valance are for 1970 cuda only. The short bracket version is for 71-74 cuda parts.
The picture you show in the first post has a set of reproduction quarter skins and a Sherman rear valance. The brackets I had (OEM from my car) lined up nicely with the rear valance on my car. I did have to push the valance up to the brackets slightly, but it wasn't like anything was in a bind or anything. The valance has a tendancy to swag away from the rear crossmember because it is so long. Can you push it up slightly to bolt up with the brackets, or are the valance hole locations off to the left or right?
Hope this helps...