Can you help me get 12's in the quarter and 15 mpg or better?

What axle? 7.25" you'll break in no time trying to race it. 8.25" is fairly strong and has a variety of gear sets available, long term racing with it and slicks make it questionable. 8 3/4" with either 742 or 489 case will suit you well. You don't need a Dana 60 for 12's unless you come across one at a good price.