This build is going to take a little bit of thought to get right, and I'm trying to minimize the amount of irreversible changes I make in case they release some updates that are better than my efforts!
Outline plan is to fit a small screen behind the display, a pi zero up in the upper module, electronics to all the buttons, switches and dials so they work and click. A speaker on the radio module and working lights seems easy. Working geiger counter gauge with simulated radiation bursts.
Top module - remove the button support post to fit in the pi zero behind the black divider - will just fit! Make the top button a proper clicking push-button,
Screen in the main module - getting on the right aspect ratio will be tricky and there is not much room to oversize and crop one. Could go a mini LCD screen or e-ink - both have their pros and cons.
Holo-tape deck - The button really needs to be amber and glowing as this is a major discrepancy between the prop and the in-game version that can be fixed with electronics. If possible a working numeric display would be cool, but there is not much space to play with - perhaps a tiny e-ink display would work? To be decided.
Geiger counter module - add a rotary encoder to the dial and maybe make it possible to click as well (using a rotary/push button). The three small buttons should be active, and clicky! The geiger counter module may be best built up on the side plate which may require trimming of the thin plastic bridge on the molding to allow it to easily slide inwards. The external wires could be commandeered to carry signal, but will probably just leave them cosmetic (or see if I can make them part of the fake geiger counter)
Twin vacuum tubes/bulbs - need to get these working, either mini-bulbs for the proper effect, or LED and a 3d printed faux bulb.
Radio module - speaker to fit in the slot, working dial either a pot or another rotary encoder (this gauge has stops on the rotation due to the radio dial bottoming out so may be better as a rotary potentiometer with physical end stops, unlike the upper one. Contacts on the rocker button so I can read it's state, and perhaps illuminating it when the speaker is on.
Battery initially a power bank concealed in the cuff, since there is plenty of room as my forearms are not hulk-like and it will be quick to change should it run out (raspberry pi could be in here too if the top does not work out).
Repaint and weathered to match a lifetime of wasteland abuse - maybe mimic one of the in-game skins.