Not able to give advice but will share my thoughts with you

The st170 seems a bad idea to start with, engine too much trouble, gear box also, and the interior would look naf in an escort, and its expensive.

Either buy a mk6 escort 1.8, cheap and the engine and box go in easy or a 1.8 or 2.0 focus all can be had for a fraction of the price of a st170
Get it running then use the money you saved and buy the motorbike carbs or bodies and a better exhaust if required

If you want to fit Focus leather seats a complete set can be had for less than £50

Now if it were me I would buy a 1.7 Puma rotten and cheap and use its engine and box etc, a lot more work and something different but worth the effort