The strips are spot welded. These spot welds will need to be drilled/cut out then you can use the same holes to spot weld the new angle strips in place. I did the new welds from the outside of the bed side which provided more access to finish the welds off. Some of the new welds are under the fender and do not require the same level of finishing as say those few which are not covered by the fender.

The angle strips from the various suppliers are what you want.

Be sure to note the vertical location of the angle strips before you remove the old ones so you know where to position the new ones.

I used a 3/8 spot weld drill bit but there are other styles of bits/cutters available that will do the job. Check ebay for some options. You will need to drill completely through the bed side from the inside surface to remove the welds. To hi-lite the weld locations I ran a knotted wire wheel on my grinder along the vertical surface of the angle strip. This made locating the welds easier.