Personally, i think you are going to too much trouble, if you want the 'ST170 look' and save the hassle of swapping the engine, then you can get hold of all the bits and bobs for reasonable money.
EG:

ST170 Front fog lights
ST170 Head lights
ST170 17 inch wheels & tyres (personally I'd go for the 17 inch MP3 wheels they look better)
St170 Lower bumper grille
ST170 upper grille (or go for the chrome grille off the 'collection' model)
ST170 half leather interior

all these come up on ebay from time to time and will be a lot easier to fit!!.

you do what you want to do though!