I received the new brackets to correct the defective end-wall column a couple days ago, and this morning was the first chance I’ve had to get out there and install them. It turned out to be pretty simple, just measure, drill and bolt. However, because of the slight difference in angle, the building was a little out of square, and moving these parts up required loosening some cross-support cables and nudging the steel a bit. The bolt-on bracket sits just 5.75 inches above the incorrectly welded-on bracket.
Now the end-wall siding will go on without any special changes to the screw pattern, which will help reduce the difficulty of installation.