yes it'll work but it'll be off. if you have the I4 and want a tach just goto the junk yard find a gen2 camry LE with the tach and put that into your car, that's how i got a tach in my I4 that didn't come with a tach
yes and as atobe mentioned calibration will be off. i remember someone did that here recently. RPMs were either too low or too high by 900. speedo was also off too. to answer your Q though, yes it will be a simple plug and play.
Like the others said - go get the cluster from a 4-cylinder with tach. It will plug right in. You can also simply swap over your speedo/odo assembly and you can keep the correct mileage on your car. Swap all the cluster illumination bulbs to red while you are at it for additional coolness.