I appreciate everyone's responses here. This forum is such a great learning resource. Kutter, I would have never thought about the hooks being spring tempered so they snap into place. I can imagine the additional skill needed to prepare them for that (shaping plus tempering). Stephen, the photos and description you provided are excellent (thanks to Stan for posting them)! I also found this example on the internet, another way to deal with concerns about scratching the gunstock:
Here is the webpage I found it at: https://www.internetgunclub.com/archived-forum/posts.php?topicid=878
I'm feeling pretty inclined to use this type of sling eye on my project, and probably attach a simple leather sling with 1/4" rawhide. If I do, I'll post the results here. Thanks everyone!