I've sold them for as much as $1,500 - so restore the one you have!
Don't worry about the stampings on anything, you can't see them anyway once its installed.
Fill the rust on the bars with Icing & high build primer, they will look brand new when you are done.
The lower spring plates are available occassionally on ebay, although not always the precisely correct versions. These later versions were just discontinued a few years ago by GM. They can be modified to match the originals, or just swap them out when you find the original style. BTW, they are RH & LH specific.
The clamp/bracket that holds the ends of the sway bar to the spring plate are/were still available by GM, they are not hard to find - bushings too. BTW, use the correct 5/16 bolts not 3/8 - even though the 3/8 size will fit easily into the holes, they will snap when you tighten them because of the sway bar stress.
The lower bushings in the vertical bars can be easily replaced with part # 31010 from Motormite (they are about $5/each!). The ID" of this item is a tad too large, so just cut it down a little with a straight blade.
http://www.dormanproducts.com/p-25927-31010.aspx
The upper bushings in the vertical bars are pressed in, and are not easily replacable. They don't usually wear out or deteriorate, but if yours are bad, we can find a replacement - would be a fun excercise!
Good luck,