You will have to join All Metal Shaping to view the pictures in the link below, but this thread is of a 41 Chevy pu where the area above the rear window is replaced to get rid of inside deep pitting, also includes roof repairs and rear cab panel fabrication and replacement. May give some insight to the job.
Regarding the warping from welding, that issue gets fixed by planishing, and is covered in the MIG welding tips and tricks sticky at the top of the page here in the paint and body shop forum. Looking at this link below, you can easily see the results of proper planishing of the weld.
https://www.allmetalshaping.com/showthread.php?t=19718
