Leave the inlet alone, the st170 system would never work, you'd be better off just dropping the whole engine, loom and ecu in.

Put a set of cams on your standard engine, better exhaust system and filter should give you 15-20ish bhp. Strip out the interior to make it lighter costs nothing and gives you better everything, put an st170 brake setup on it and some uprated suspension so you can stop and go round corners quicker.

Having a quick car isn't all about the engine, do the free / easy to do things first!