What should i change to get into high 11's?

My wifes 360 Dart is full dress,close to same motor as yours, has 4500 Hughes converter 4:30 gears, and 28"x 9 1/2" hoosier slicks.Stock springs with snuber.
It runs 12:10 @ sea level, and 12:40's here @ 4,000'
It's going to take gears and a converter to get where you want to go. 4:30's will be barely streetable though with a short tire.