Thanks for the inputs, folks. As mentioned, I did query our local FSDO. Once we got on the same page, here was his response:
There is no 337 required for welding. Welding is a process of fabrication. A 337 is required for alterations and repairs to the product itself. The welding must be done iaw industry standards. Don’t get wrapped up in the reinstallation of a channel. As long as the weld does not compromise the tubing structure, and it is done correctly, you have not done a major repair to anything. I believe people are over-thinking this issue and making it way too difficult. There is no interruption needed for this specific issue, it’s very clear...
If you do not agree with this, make a written request to the FAA. I would send it certified return receipt.
Federal Aviation Administration
Office of the Chief General Counsel
800 Independence Ave, SW
Washington DC 20591