He also probably had a 3:73 rear end ratio as well (very popular among the LS1 owners)
12.4s in the quarter mile you said.......well, he need at least 530 hp at the flywheel to achieved that time at the track without slicks or roughly ~470 hp with them.
I don't care so much about his mods......all he needs he's a good set of heads and a good cam as well. That's all.