With the supercharger you will get those gains on a good stock engine with a decent exhaust system. 2.5" works well.
Mine with a flowed head and full exhaust with the DBilas manifold and 200cpi cat went over 280bhp first time on the dyno! only safe to 270bhp max so it was restricted back until I forged the bottom end.
Max88 performance (Aylesbury, Bucks) sells kits as does Jeffery Reyland Nelson but he is in USA.
@[deleted] aka Carl Evans can fit it for you he is somewhere in the midlands area? Courtenay Sport are the only ones in the UK who can map a Z22SE with standard ECU, they are in Norfolk.
The super charger kits to buy and fit yourself then have mapped comes to about £1500 all in
Decent cam kits will set you back £700-£1000 alone and still need mapping to get the gains, and still you will only get to 170ish with a flowed head as well.
My advise would be to get it well serviced, replace full exhaust system including the manifold then meet a few people with supercharged 2.2's. It's the cheapest way to gain power on these engines.