That's really a good choice, other wise you would need two transistors and a few resistors. The problem is, the transistor by itself inverts the signal.
Part is trivial to use. Vcc connects to +5 on the computer end and Vcc connects to +12 on the vehicle. Tie all unused inputs to ground.
Connect the MODE pin to Vcc.
There is a dot on the IC. That dot is pin #1. If you orient that pin to the bottom left, Pin #2 is the next pin going in the clockwise direction and continuing around the IC.
The problem may be the package availabe. DIP or Dual Inline Package has pins.
Now we are only guessing that the part may work. we know little about the computer's signal and little what the tach expects.
The tach may expect "a contact closure to ground" or a "switched +12 signal" and sometimes is selectable.
We know little about the currents available sinking and sourcing on the computer side and the amount of current the tack is going to consume. It's only a guess whether the circuit will work.
We also don't really know the locic power supply for the computer, but are asuming it's 5V.
I'm sure we can walk you through some ideas, but it's difficult because the constraints aren't well known.