A single 16.2 second quarter mile is one thing--repeating it 5 times in each direction on the same stretch of road is quite a different story. I'm not trying to fan the flames here, I'm just telling you that a single run won't cut it unless you are on a dragstrip. A single trip down a dragstrip IS RELIABLE, because the dragstrip is a flat (and hopefully smooth) surface. In other words, you are testing in a controlled environment. The G-tech is quite accurate in its measurements, but unless they are done in a controlled environment, the numbers are quite meaningless. In order to rule the slope of the road, wind assistance, etc. you need to do several runs in rapid succession going in opposite directions on the same stretch of road, and then take the average. Even then, if the road is bowl-shaped (downward slope at the beginning, upward slope at the end) you will get lower numbers both directions than you would on a flat road, b/c you are getting assistance from gravity off the line, where you need it most.
FWIW, I have done a 6.15second 0-60 run in my SHO, but that number was meaningless because the road had a very slight downward slope. When I turned around and ran the opposite direction, I was well over 7 seconds.
Having said all that, I don't doubt that a 16.2 sec 1/4 mile is possible with a lightly modded Vulcan, especially if the trans is in good shape.