Thanks guys! Well earlier I had joked that I was worried about digging into the quarter panels further and it's amazing what people do... I used some stripping discs to strip off an awful lot of body filler to find the reason there was so much was that they never ground down the spot welds. So they just filled over them, seems like it might have been easier if they would have taken some time and finished the welds properly. Here's some photos of what I've found so far: There was filler over the seam, it never looked right, it looked off. Now I know why, all of these welds were not dressed and had to be ground down before I could drill them out.