This doesn't directly answer your question but it sounds like it will save you A LOT of tedious work.
Why re-invent the wheel when you can buy a quarter panel skin and inner quarter panel extension with the correct curves/creases and sizes? Even if you don't use the entire new quarter skin, it's got the right profile regardless where you cut it to weld into your existing quarter panel.[/QUOTE
I know in a perfect world thats a fine idea, but holy crap try and buy one that fits right. they all don't have the correct curves/creases and sizes I did buy the quarter that goes from the door to the bumper,then i sent them back cause they where junk, then the next set went back,, finally I had to keep the 3rd set cause I was lossing way too much time so I had to cut them apart and use only the areas that where bad. The front part I could use the body line on the door to line the body line on the fender up. But have no reference point on the rear part. However thx fer the heads up on the inner extension I forgot you can buy them .
thx for the help.