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.
Had words with Nick Potter - the caterham specialist I use- about improving torque and power and his comments were to put in R400 cams (and then get Northants to do set up to keep torque at around 4k revs which I haven't done yet .) Supercharging is a very good next upgrade , possibly next year , power is then at mid range rather than 7k revs - 30% increase in power allowing for 20 bhp take up by charger ?
