Mounting a circuit board atop the Victoreen 710-104 ionization chamber requires figuring out the location of those 6-32 studs:
Given that it dates back to the early Cold War days, the bolt circle dimensions are all hard inch:
I embossed the studs into a pad of Geek Scratch Paper, eyeballed the stud-to-stud spacing from a cheap ruler, back-calculated the BCD, rounded it from 2.742 to the obvious 2.75, then fed that into the first BCD calculator that appeared in the obvious search.
The can is just over 3.5 inch OD and stands 1.5 inch tall.
The can will run at +24 V in relation to the rest of the circuitry, so the studs must be insulated from the PCB’s copper pours. That, most likely, will require some 3D printed doodads.
The circuitry must live inside a grounded metallic can that excludes random electric fields. Somewhere in the pile, I have a few sheets of Mu-metal that, while grossly overqualified for the task (even without heat treatment), should solder up nicely…