[squidtone]

Hi,
I agree, yes, that side to side brace gets welded to the wheel well. Don't forget too, that GTO's had the small triangular piece....Pontiac called it a "filler"
So that filler gets sandwiched in there too.
I remember when I did mine, I did have a pretty big gap. I had to massage the thick brace flange piece to fit better. The trunk pan flange require quite a bit of massaging around there too.
Clamps do go a long way to help....and once you start on one end, a body hammer brings the rest in really nicely. I love how steel moves and bends!