The best way to get low end power for your car with a normally aspirated A series engine [which isn't really what you asked for] is to use an A15 engine. These use a 3mm larger bore,which isn't the important part, but they use a 12mm longer stroke, & this is the real secret to it all.
That's a half inch stroker over your A12 engine & that translates into torque, which is what low end power is all about.

Even a stock A15 will out-torque a mildly modified A12 at lower speeds. The upside to switching engines is that the A15 comes with the bigger port & bigger valve head to begin with, so there is more scope for improvement once you grow tired of a stock A15's performance.
Even the A14 with its 7mm increase in stroke will offer a very usefull improvement along with the better cylinder head.

Have a think about it & do the maths before spending any money.