If you fit a 400bhp, 400lb/ft engine to a 14+year old car, dont forget you will need a lot of other work done to the car, ie poss shell strength mods, proper brake setup, proper suspention kit, poss new bushes all round, and dont forget the biggest problem, the gear box.

As rudey says £7000 for your build, then gearbox of maybe £1100, etc.. you could easily spend £15000 on the upgrades.