Just did this on my sedan and it worked well.
But instead of cutting up the frame, when i flipped the mount upside down i noticed it would fit perfectly in the grill. But the holes where offset slightly.
So i thought about using some nuts, washers and long screws.
So i looked around and eventually found some Crown Bolt wall mounts.
(
http://www.homedepot.com/prel80/HDUS...4+4078&pos=n20)
They worked perfectly. I think if you put a little Loctite on there it wont go any where.