The thing is an ST170 engine started life as a 135bhp blacktop, so it has 35bhp overstandard already. ITB's usually give gains on their own of around 40-50bhp on a 2litre engine with cams so your only really looking at power levels of 185-190ish once you have removed some of the stuff that gave it more power in the first place to fit the ITB's
Listen to Tabetha he knows his stuff, aftermarket managment is not cheap but will get the best out of what you got and if you switch to forced induction or ITB's in the future then your managment will be able to handle this already unlike the standard black oak