7 1/4 Sure Grip rear end value

The SG is worth 250-300 and is the value in your rear end. The rest as you say has little value.
Now that is if all the internals are good. Finding parts is impossible. Last one I had the spider gear cross shafts were broken. If your going to sell it, I would take it apart and inspect it. If it is good take plenty of pictures to show the potential buyer that it is good. That will make for a quick sale.