Twister2gt

This weekend i installed new bushings ball joints and i noticed that my frame rails are starting to rot out. How hard of a project would this be to fix. I know how to weld. Would i just have to get replacements off another car and weld new ones in? Its not a huge deal right now but i think i want this to be the next thing i do. And buying another roller and scraping this car is not a option its a twister II and i dont want to let it go to waste

86 5.0L

since you know how to weld, buy a wreck(with the frame rails straight) and cut and weld