Originally Posted by tech69
before you do any of that measure the distance between the top and bottom lines of the left and right quarters and doors. If it's the quarter the distance between the uppers and lowers will be shorter on the right quarter. If you put tape right on the peak of the body line it will help the measurement be accurate enough where a clear discrepancy will jump out, that is of course if the aftermarket quarter has a bodyline that's pretty close in roundness to the original on the driver's side.
So if that's it and you still have the original quarter you can do an awesome open butt weld repair. If not, I would try to use a mini air saw due to the blade being thin so when you cut out the piece you plan on reusing you will have more metal on it. an air saw with a sawzall blade will give you more control for straighter cuts.
you can also cut out your quarter with a spot welder bit for the plugs and and carefully use a cutt off wheel for the welds at the flange up top but you probably won't be able to just loosen the front and bring it down. It would have to be the whole quarter, and you would also have to figure out why it's not going down...wheel house? Flange to rocker ? door jamb opening bend to rocker?
Sometimes the corners of the flange that tucks under just needs to be snipped cause there's not enough room in there for it, or just bend the corners. Sometimes it's the door jamb bend that goes to door gap to rocker gap. Just have to figure out why.
I can check those measurements easy enough. The quarter on the drivers side is new, too, but fits well. I will still give some of the door adjustments suggested earlier a try to see how much I can 'minimize' the discrepancies and see if it's something I can live with. And I need to study that area for feasibility in the event I need to knock out the quarter ornament section to fix.