Here the circuitry to display the score has been added. It uses a 7-segment LED decoder to convert the digits into segments that can be displayed on the screen with some logic. Some additional logic makes sure that the decoder's blank input is low if we're not in the correct place on the screen.
Four multiplexers (2 dual multiplexer chips in the original circuit) provide the input to the decoder depending on the horizontal position. This circuit relies on the fact that the decoder chip (a 7447 in this case) turns off all the segments if the inputs are all high.
You can change the score by clicking on the inputs at the lower left.
Next: The Ball.