You wont get 30bhp on the standard inlet manifold, you will have to fit individual TB to get over 200bhp which will cost you fitted and mapped with new cams £3000+
I can almost garentee your ST170 will not be running anywhere near 170bhp it will probably be in the 155-160's most of them are.
I have spent well over £2000 on bolt on mods for my ST170 and im only getting 189bhp last time it was RR'd
Unless your willing to spend that £3000 or £7000+ going forced induction it i would say your wasting your time.

With regards to your clutch change, you have an early ST170 with the smaller weaker clutch, make sure they fit you the later larger type, and the dual mass fly will need changing along with the slave cylinder, if you dont you will only end up doing it all again very soon.