OK My opinion. 12's are viable normally aspired, with a lightweight car. If I were doing this project, and not worried about the money, and had the "brain power" of the site, available. Normal block prep, with some oiling system mods (external belt drive pump/wet sump). K-1/Ross piston combo, Mike Jeffery head. Electronic port fuel injection/ignition. Charge cooled turbo system on E-85. This is just basic points, details on CR, boost, cam, etc to be worked out. Should be able to run low 11's high 10's reliably. Just remember the body/chassis needs to be built to suit these speeds, also. Speed costs money, how fast do you want to spend it?
But a 12 sec car, can be done relitivly cheap. My 66 Valiant runs 13.5's, and only cost about $1500 to build, including buying the car.