hi mate
from what i can see (im new to cosworth) its cheaper to buy a convertion i think if you just want a small increase on a 2wd then stage 1 is chip filter and exhaust and gives 270 bhp and that changes ignition timing and fueling. my 4x4 has a stage 3 setup which from what i can tell is bosch 803 green injectors 3 bar map sensor t34 turbo exhaust panel filter and stage 3 chip and this should give aprox 330 bhp.
i bought my car like this and im very impressed and it all seems alot cheaper and easier to get this power than it does with a jap varient.

just my 2 cents