Swapping out non working speedo/adding a radio

The bulb sockets have 2 tiny tangs that hold them in the board. Their electrical contacts make opposing pressure. Plastic gets brittle with age. They're not all as old as my 67 model. I can't predict when yours may start falling out. Some are a lot more difficult to access from underneath than others.
I searched the web for the best price on Standard brand sockets. Can't recall what vendor I ordered from. Wide range of bulb types and sources. LEDs could last longer than the car.
Clean the board contact points with most anything from a pencil eraser to Maguire's All Metals polish. Every screw that attaches the board to the housing is a ground contact point for bulbs. Gauge mounting studs and nuts are conductors too.
Power screw drivers can damage things. Careful not to overtighten any of it.