This is the top side, the one that mates with Darthcam. You can see the hold-down screw and the registration pin offset from the center. The two big holes are where the tripod adapter plate screws in from the bottom-- they go all the way through because it was just easier that way.
Bottom side. This is where the tripod mounting plate screws in. You can see the nifty double hole in the bottom right corner-- this is a fix because the first tap I was using broke off in the hole and I ended up just filing it flush with the middle plate because I couldn't get it out, and had to drill a new screw hole.
You can also see the access hole for the camera hold-down screw just southwest of the left tripod mounting hole. It's a 5/32" button-head that's completely captured within the assembly. I think it's damn clever. It needs a hex wrench to release the camera, but I have one specifically for this and it lives in the camera case.
I also broke off a #43 drill bit in the aluminum in the bottom left corner. I could have pulled that out and continued with the hole where I wanted it to be, but I ended up drilling a second hole and using that one instead. I'm a dork.
The hole to the right of the right-hand screw hole is for the registration pin on the tripod adapter plate. It goes on one way only.
Side view. Here you can pretty easily see the three-layer construction. Each layer is 1/8" thick. The whole plate is 5 inches by 2 inches. I'd have rather made it out of one piece, but with the tools that I had available, this works.
The first coat of paint went on today, another coat tomorrow. I'll try and get some pictures of the whole thing assembled and mounted on the tripod after it's finished.