How would you repair this frame?

[Rocket3]

Is it repairable? I have a SWB,coil spring suspension frame with some severe rot where the coil springs mount. The vertical section of frame rail is pretty thin and cracked on left side. Right side is just thin. I was thinking of adding a plate on outside to fix that. The horizontal bottom sections of frame rail have a curve to them. I was thinking of cutting out the bad and welding in a new piece,but how do I match the curvature? Will heating to bend the replacement piece with oxygen/acetylene torch weaken the metal? OR.. Should I find that section or complete rear 1/2 and weld it in? No-Limit has a kit that replaces the ENTIRE rear portion of rails,but it is $1,100 and requires bed floor to be raised 4",which I don't want to do. Does Porterbuilt kits replace any of what I have that is rotted?