For my next tacho I have converted the circuit to DesignSpark, and used the output to make a VeeCad Veroboard PCB. This new board has the components for 2 digits, but is designed to string up to 3 boards together, for up to 5 digits with the program I am using.
Just leave out the components for the 6th digit. It has the digits mounted separately, and connected by plugs and cables, for greater flexiblity and ease of construction. Each PCB includes a 4081 quad AND gate to allow the displays, including decimal points, to be dimmed via PWM.