I don't recall having any issue with the thickness of the wheel arch panel. I cut it right along
the lower racetrack molding, so I didn't have to do "too" great a job welding it in. I did get
some warping on panel above it, so stitch weld it sparingly, and let it cool between weld sets.
Also, don't force patch panel to meet 1/4, which is the other reason I think I have some warping on
1/4, right above the weld points. I never cared, always assumed I could someday get quality 1/4's, but that
may not be the case I guess.
Some random pics of work I did back in 2010