Frame bracing? Converting to disc brakes?

[Egdorf]

Hi, I have a couple questions.
First, I have started the build on my 68 C10 stepside. I found a brace on each side, riveted directly in front of the coil spring pad to the side and bottom of the frame. The problem is rust developed in between these two spots, and actually pushed them apart. I attached a picture. Keep in mind that in the picture the frame has been flipped over so you are really looking at the underside. I'm knocking out the rivets and taking those plates out, straightening the lumps in the frame, then painting and bolting back in the plates. I just wanted to know if anyone has noticed these before, and/or had the same problem. My guess is that these braces just gave some additional frame support by the springs.
My other question concerns brakes. Since I want to make this truck go fast (some day) I want to upgrade the drums in the front to disc. I don't think I need fancy aftermarket brakes, stock will do. Do the later year stock Chevy disc brakes work with the stock spindles?
Thanks for any and all help.
Jerry