I had similar trouble with my 67. Do you have the 1/4 welded in yet? I had adjust how the 1/4 was attached to the taillight panel to force the curves to match. Also the bend wasn't sharp enough so there was a large gap between the 1/4 and the extension. I ended up respaing the bend by building the area up with some fiberglass body filler. Probably not the strongest approach and the fit isn't perfect but it looks okay.