Okay. Here it is. I got ahead of myself with the making and didn't photograph the rivet process.
Here's the back.
So, how do you get the rivet holes to line up? I taped the front and back pieces together after drilling the 3 holes in the front piece. Then I drilled one hole using the front piece hole as a pilot hole. Then I pinned through that hole with an ordinary dress pin, nailing the assembly down to my bench. Then the next hole, and pinned, etc. This helped to prevent drift so that the holes aligned properly.
For rivets, I used tiny brass nails from Micro-Mark. You can make your own, too, from wire, but it takes a bit of fiddling to get one end flared before assembly.
Next, what sort of necklace? I have a sort of style-feeling in mind but nothing specific. Should it be the African pottery beads, the Indonesian striped glass barrels, the antique African iridescent Ougougou? The rough leather is a strong element. I don't want to diminish that with an overly decorative approach, and there's scale to consider, too.
I may settle for a handful of mismatched black beads wired into a fine chain, rosary-style. And then there's another beach rock, a fine subdued red that really seems to belong.
Today's the day to finish the piece! I'll post the results when done.