In 1970s a large scrolling LED / neon sign would use a bunch of shift registers as the backing store and the scrolling mechanism. You only needed 1 bit; likely in 1980s you could add another bit (for red and green). This approach makes the display highly modular.

The input likely would have been a punched card for a fully bitmapped display, or something more complex for a character-syntherizing display with a ROM inside it.

In late 1980s you'd likely already use a 8-bit CPU and a bit of SRAM, with scanning.