Jim,
People were doing that years ago. Tony Pizzi comes to mind. He had the baddest 68 Z28 in the country.....and the rear bumper was filled with lead! Not as much today because you'll get wacked big time by NHRA and have your name and photo on the cover of National Dragster for flagrent violations.
NHRA does not check rear wheels on the scales, only the full weight of the car after qualifying runs. We were checking my new car to see where it is. Will be nearly impossible to make it 50-50 at D weight, maybe E weight as I would have to weigh 3260 lbs adding over 150 lbs to the weight of the car.
I didn't take the NOS metal on the new car and have it acid dipped. Just couldn't do it to that NOS GM sheet metal. All the mounts are in the stock location too.
In 2004, I got to go to the tear down barn at Indy for winning class at the 50th NHRA US Nationals. Believe me, that experience will get your attention. They check everything and even have sectioned factory cylinder heads on hand to check for acid ported heads.
Check out our link:
http://www.z28camaro.com/race.html
Jerry