Take pictures first lots of pictures, use a 4 1/2 grinder w/ thin cut off wheels. Then cut only where you want to weld the new stuff to. Save what you cut off to use as a guide. Then only cut out the rusted stuff in like 6 or 8 ins. each.Don't be like me an work on it all day long, take your time,make it last a few weekends,enjoy the pain.