Ok cool. I know i would love to tear into it and change out the rusty structure. I guess i must be a masochist. I do sheetmeral structural repairs on aircraft for a living. They get quite corroded under the galleys and lavatories, changing out corroded out frames , stiffeners , and stringers are a way of life for me. The darts rust is a challenge. Take your time, i have seen far worse rebuilt. I followed a thread here where a guy was holding onto a Truk Lagoon rusty 67 barracuda 383 4 speed convertible because he was waiting for all the pieces to be repopped. I watched him work the carto completion a section at a time. It was impressive. I believe he started in the middle as well.
I recommend getting some 1/8" draw type cleco pins with the wing nuts. "Brown tool supply, or the yard aviation supply" . This will help you pin and hold stuff together prior to welding, then just remove the pins and weld up the 1/8" cleco pin holes when done