To answer the original question....

Correctly specd Engine & Turbo.

Management, Mapping, Major Headwork, Cams[oops Im thinking ZT again] Cam [blinkered off] , Steel Bottom End, Clutch & Box that are man enough.

Im sure there is loads more, to easy to forget.

Is it worth it?.....that all depends on how Passionate you are about your RST.

It could be said why spend ^^^^^ £5kplus easy & the rest when you could have a Subaru, Pulsar GTiR etc etc for modification money.