I was puttering around in the garage today and decided to see if I could get the right side rail to fit any better. It doesn't quite lay down flush with the gusset that's right in front of it. I thought this may be caused by a tiny bit of interference between the two pieces, so I drilled out three rivets, pried it up a bit, filed the end slightly and riveted it back down.

Nope...no improvement. Time for a nap. :-)