Calculated HP for rear wheel HP would be approx. 170HP and 190HP, only about 20 HP difference, so 275 injectors would be more than the difference. If your looking to just up the ponies a little get a mild fueling and timeing box and reap the benefits of more HP and better fuel mileage. With the auto transmission you can not go much over the mild boxes without causeing harm to the transmission.
Ron