Question on Bed Rails ?

[Bob the Builder]

I started working on my 56 short bed on sunday and I ended up tearing out the old rotten plywood in the bed,the old rails were in pretty bad shape and I cut the whole mess out of the truck.My Question is about the right angle rails on the right and left sides of the box.Are those rails spot welded to the box and how do you replace them? What if I use ss rails and finally any suggestions on where to find replacement rails and hardware? Also I would like to use hardwood, not plywood on the bed. My second Question has to do with lining up the bed b4 its bolted down,any information is really appreiciated.