Jeff,
I mounted mine behind the original radiator support and welded it to both the front frame rails and the original radiator support. You shouldn't have any issues with the valance. I am going to have and drill and tap two holes for the bracket that holds the hood latch and connects the top and bottom of the radiator supports (you can't fit the stock J-nuts in there anymore). I'm not sure if the stock radiator will work or not (I'm planning on running an aluminum radiator). If my radiator wasn't buried in the back of my storage shed, I'd try and see if it would fit. Perhaps with these pictures, you can go look at your car and see if your radiator would interfere with the brace? My radiator has been out of the car so long I don't even remember what the bottom looked like when it was mounted.
Anyway, this is what Peter at XV Motorsports sent me on the radiator support:
"It will mount one of three ways.
1. Side tank radiator, should fit fine IN PLACE of the original rad support.
2. Mounted BEHIND the original, between the K frame and the orig support with extra tubing we can send to extend it.
3. Again, using extensions to make it longer, in place of the orig rad support to clear the lower tank of a factory style radiator. "
Those directions didn't really make much sense to me....
However, I think mine is mounted the same way as the picture on XV Motorsports webpage shows.
Anyway, here's the pictures... the brace did fit perfect right where it went....
Travis
72 Cuda