I did them on my 'vette too... (also had them on my '93)
It is far cheaper to just have a local shop put them on. A good muffler shop can bend pipe up for far less $$$ than those eliminators are, and you can have them mount them however you like them (as far as how the line up with the car/bumper, etc.)
With a 6-speed, I think resonance is only bad a low RPM's... like when running in the wrong gear for the speed. (say, 6th gear, 45 MPH while trying to accelerate).
Take note before hand that the exhaust tips matter... round tips will produce better sound, the rectangle tips tend to choke the sound down some...
The pipe size also matters. If you put a larger pipe on, you will more sound, smaller pipe, less sound. For maximum sound, you would go from smaller to biggest pipe (think megaphone). it will also make the sound 'smoother'.
I think the last time I did mine, it was $120 out the door, using the factory tips off the car. my '93 cost roughly the same, including new tips (chrome slash cut duals on each side)