ORIGINAL: Old_Goat
Headers, drag radials, tune, and a stall (what rpm?...3200?) in a 425 hp car should do way better than 12.9. I am thinking 12.0-12.4 depending on track conditions and DA, plus some good break in time.
You're forgetting this car is overweight. There's more to it than a flywheel number. At that weight, trapping 109 (weak for the mods), it ain't going to run a low 12. An LS2 GTO? Yes. A so called "hemi" Challenger? No.