After that, I posted up on the LCML, asking for advice on how to mount the spare carrier latch. I got a lot of good suggestions; in the end I cut openings through which I could install nuts and washers onto bolts. I was thinking of welding nuts in there, but wanted to make sure I had a little slop in order to position the latch just right. It was late, I was tired and this project was already taking WAY longer than I planned.
Due to parallax of the camera angle, it doesn't look like the cut-outs line up behind the holes. They actually do.