91 lumina tachometer

i have a 1991 lumina euro with a 3.1L and i want to put a tachometer on it. the problem is that I havent the foggiest clue as to how to actually do it. i am not concerned with how it looks when its down I just need the instriment to actaully be there and let me know what my engine is doing. any advice or instruction would be greatly appreciated.

-thanx,
dave