Man your numbers are way off... 6K more for a v-8? You can get a 99 GT for around 3K more than you are paying for that sixer. But the 8 only has 260HP. With the mods you are suggesting you won't get to 235-255. You might get to around 220 at the crank and only about 175 at the rear wheels. Keep in mind that just because a part claims 10HP it doesn't mean you can add a 10HP part with a 30HP part and instantly get 40HP. You can get decent numbers out of a sixxer, but its going to require a power adder unless you plan to dig into the motor. But for a quick, cheap gain, just add nitrous. But over time, nitrous bottle fills will add up.