[84LX89GT]

The new V6 mustangs i've heard of getting mid 15's in good weather/slicks and 5 speed, but most are high 15, low 16 from what i've seen. they also have 190 horsepower. the older ones with 145 horsepower are low 17 second cars which is a little slower than most non-turbo imports. Heck, my jeep can almost beat miatas
For 400 dollars i would definately invest in gears, the difference is HUGE. 4.10:1 gears may be a little steep for the powerband of your engine, let alone the grip of your tires. 3.73's would be my recommendation and a set of good sticky street tires (or drag radials on back).
Other than that i wouldn't bother modifying anything until you get some ported heads/intake manifold (i've heard that the pre-99 split port heads flow more ported than a ported set of split-port heads so you didn't get the total shaft for your model year V6), then you can start making some serious power if you chose to.