As mentioned earlier i used a 8-Bit expander which can be controlled by I2C. This may cause a problem with the adresses because they are all the same and you´d end up with e.g. only the minutes on the display. To solve that problem i added 3x3 array of male pin headers with jumper conectors to connect A0-A2 to Vcc or GND to change the adress for every single expander invidually.
On the right i added ports and a nice spot for a N-Ch Mosfet to control INS-1 tubes in case you mis something to seperate the numbers. The connectors on the side are pretty smart in my opinion. You can solder them one to the next or use headers to hide the control unit behind the display unit. The resistors are 0805 and the 15k ones are 1206 (you can still solder 0805 on the pads)I added in the edges M3 screwholes in order to mount it permantly to a frame.