Don't waste your money on a set of tweeters for the car. Instead, buy a good set of 6.5" components and place them in the stock locations.

Time to give away a secret (well not really a secret, but something that most people do not understand)

Wire your passenger side woofer out-of-phase and the rest of the vehicle's speakers in-phase. While this will put the car "mechanically" out-of-phase, it will put the vehicle "accoustically" in-phase, thus giving you mid-bass.

This has been a proven technique in the competition circuit and will work for your car.

Good luck to ya!