For 170bhp out of a 2.0 zetec, you'd need a good throttle body kit, plus 4-2-1 manifold and full exhaust after that. That alone is £3k mate.

Personally, I think you should buy the escort, fit the 2.0, and then see if you need more power.

All the info is available on Escort Evo, and you can use all the standard Ford parts, so no nasty chipped 1.8 / 1.6 ecus to correct the fueling

What BMW do you have at the moment? The escort will be faster than a 320i