Hi ! The speedometer implementation uses the tone library which can emulate frequencies from 31hz to 8Mhz. I let you do the convert it to pulses per miles
, from my experience it will cover from 20kmh to any speed you want.
Concerning the signal shape it's a 50% duty cycle square signal.The voltage will be of 5V at the output of the arduino, or can be raised to 12v using a TIP wiring.
In order to plug both tach, speed, boost & dot matrix on the same arduino you will need to choose wisely your pins for the boost (the tone library steals arduino timers which breaks PWM used for boost gauge.
So on a UNO (or nano, it's the same chip) :
I would suggest this pinout :
Tach : D3
Speedo : D11
Boost : D5
Matrix, any pins you want.