First thing you need to know is that Mar-K company in Oklahoma is the main bed parts company in the business. They are a fantastic company that makes their products right in Oklahoma for a very much working man's budget price.
http://www.mar-k.com/Catalog/catalog.aspx
Just punch in your truck info and buy what you need. In this case, I punched in 71 model LONG STEP bed and got seven choices of bed strips from original steel all the way up to polished stainless with hidden fasteners. A basic steel original type strip is part number 110056 and costs 10 dollars each. This is prepunched with factory holes already.
Angle strips, prepunched with factory holes, are 36 dollars per pair. Part number 110156.
I can highly vouch for Mar-K. Several trucks I've built were with their parts. Fantastic bunch to deal with.