You'll need a little over 300 horsepower at the rear wheels to break into the 12's under ideal conditions. Realisticly 325 RWHP should do it.
Course it matters how much of a brick you're trying to move through the air.
I used to run a 69 Vette with a 406 and then put the same engine in a 72 Nova and the Nova went slower. I think the difference was about 1.5 MPH.
The 60 foot time is the most crucial part of a good ET. No matter how much HP you've got, you have to get it to the pavement.