shrinking with a torch is very tricky. i would set it out in the sun and let it heat up good and then hit it with a bucket of well water. if that does'nt help move on to the next step. buy a shrinking hammer from eastwood and try your luck. my guess would be that it's probly as bad as it can get. to torch it you need to mark th center of the warp and the outside edges. start close to the weld as this is where it started. do a fast cherry spot the size of a quarter and then hit it with water. use hammer and dolly to help relieve the warp. if you can bring the sides up the center will follow. good luck.