The first idea for the display system is a monochrome LED matrix display in the pinball's backbox.
Currently, I am planning on a 37.5x16 cm display consisting of 75x32 LEDs of the right size - probably 0.5cm diameter.
This matrix of 2400 LEDs will then be controlled by a microcontroller board interfacing the main control computer's parallel port.
The microcontroller board will possess a RAM chip used as video memory, which will be accessed as bitmap from the microcontroller to turn LEDs off and on.
The microcontroller can then, through a 32-bit wide row bus, cycle through the 75 columns using a 7-bit wide bus and demultiplexers. For this, five 8-bit outputs on the microcontroller are needed.