A total of 3 reviews of this product on Reddit.
Looks a little like the bracket off an old bed that would hold the button type head of a metal bed rail. I have some old metal beds with similar looking brackets.
eta- here’s a similar looking double claw hook for a wooden bed frame
I can buy hooks pretty easily, e.g. http://www.amazon.com/BedClaw-Hook-Plates-Wooden-Beds/dp/B004HITCXC/ref=sr_1_1?ie=UTF8&qid=1398208025&sr=8-1&keywords=bed+hooks or http://www.amazon.com/BedClaw-Retro-Hook-Plates-Wooden-Restoration/dp/B005LVMST4/ref=sr_1_3?ie=UTF8&qid=1398208042&sr=8-3&keywords=bed+hooks so I’m not too worried about that.
I’m not sure that I’ll be able to re-use the existing bed rails as I need to add both width and length.
So essentially you bolted a block into the headboard (into the existing holes), drilled holes farther down the block (to add width), and then attached your new side rails to the block? Do you have a picture? How stable is it?