Besides the IR ring PCB hat there are some additional parts required to bring the build together. I had the camera/lens holder, spacers and mounting bracket 3D printed. There is also an extra long header attached to the Pi for connection with the hat. The hat could be 5mm lower to the Pi but I'm not space constrained and I'd rather have the extra space for potential heat sinking. The small black square is the IR pass-through filter which sits between the camera and the lens. It's a glass filter and has some beautiful characteristics but probably overkill for this use case. In the image below you can see the camera holder comes together nicely, all prepared for being attached to the hat.
I realised I needed some way to mount the cameras that allowed easy aiming. Originally I had planned to use a standard 1/4" 20 camera socket and purchase some cheap wall mounts. But in the end it was far cheaper, quicker and closer fit for purpose to design something simple and print it. The mount uses bolts to clamp each axis while still allowing movement, the hold is surprisingly strong. To mount it to a wall you could use double sided tape.