When all is said and done there are only two ways to get significantly more torque at low revs: forced induction (supercharging or turbocharging) or increased engine capacity.
All the exhaust systems, "sports" airfilters, and throttle bodies will help but they won't make all that much difference. In some cases a good cam will make a lot of difference but if the engine already has a good cam, which the 2L Duratec does, a sports cam will probably only effect the top end.
Remapping can make a big difference. I had the chip changed on my Alfa 75 Twin Spark years ago. There was no noticeable improvement in outright performance but the torque characteristics were much better - many bends that had previously required second gear could be taken in third.
