Got the replacement brace this morning.
To use the whole piece would be a lot of work, so again I'm going to just use what I need. First I clamped the replacement brace to the patch panel, and scribed a line at the height of the patch panel. Then I layed a steel ruler on the scribe mark, and made another scribed line the width of the ruler below it. I layed the ruler on the old brace, and scribed it the same way. Then cut both. Next I clamped the patch panel in place on the fender, and used it to jig the new brace into the correct location. I tacked it in place before taking the patch panel back off to finish welding the brace.
I think I'll take it to the sandblaster next, while he can get inside of everything. Then I'll weld the patch panel in place.