Realistically, in a 68 Charger, he is not going to lose 1200 pounds. He may be able to get it down to 3400 pounds if he is really conservative, removes heater core, all AC components, back seat, exhaust system.
I ran a 68 Coronet w a Hemi and that is what we had to do to get it down to the minimum weight in SS years ago.
SO figure a car weighing 3400 pounds whim int. How much power does he need to make to get the times he wants?
Build a solid lower end and add a power booster, either turbo's or spray it with a 200 shot.