I finally finished the fix today. I've been traveling a bit and so this task got strung out a bit.
I'm very pleased with the results. I did decide to replace the angle. I removed the top deck which went very smoothly. No enlarged holes from drilling out rivets. Then I removed the old angle. I filled both holes (the small angled pilot hole and the bolt hole) in the longeron with JB weld. Later I re-drilled the bolt hole so that JB weld only remained in the angled pilot hole.
I fabricated a new angle and installed it. Before re-installing the top deck, I fabricated the gusset. Actually I made one for each side just so they match. It looks nicer. I then match drilled the gussets to the top deck so I didn't have to back drill through the holes to install the gussets.
I then re-installed the top deck, and finally installed the gussets.
Here's a couple of photos.