PSI

To mount the Processor Status Indicators (PSI) I used a standard PVC pipe coupling. The PCB fits perfectly in these and they have a ridge in the center that will hold the board in a good spot. Also pictures here is the dome panel that goes in front of the PSI. Not shown is a frosted disk that goes on the front. I cut that disk out of a piece of white plexiglass and glued it to the coupling. The edges will not be seen so the cut doesn't need to be very clean. 

My initial way of holding in the PCB was to cut two small rectangles of thin styrene, drill holes through these and the pipe fitting and then bolt them on. 

Some time later I got a 3D printer and used that to print a retaining ring. You can download the STL and original FreeCAD file from here: https://www.thingiverse.com/thing:4948450

To attach the PSI to the dome I used these metal plates I found at my local home improvement store. 

I cut these to length, and bent them to make a L-bracket. I bolted this to the pipe fitting and attached it to the dome with the bolts I built into the dome when I assembled it.