Hi
Yeah, good advise, get a stainless performance exahust and a good induction kit to release that bit extra to get you up to the full stage one expected 270 hp. We got these - recomed mongoose and K&N 57i, check us out on the internet....?
Try a 4x4 intercooler also, plenty used around for £100 or so - this will allow you to run a little more boost saftley (just done go mad).
The problem with the suspension is that its probably knackered, if the springs are sagging, the dampers will probably be fit for the bin if they are the same age we reckon. We've put Suierra based stock cars together with Gaz kits, dont go coil over for a road car, go for adjustable with standrad ride hieght but 25-30% uprated springs or a drop of 25-40mm max. This will give you better grip and less squat under acceleration (when the rear dips down) which will stop the car scrapping its bum - i know, had the same issue. Depending upon the amount of lowering you do, you will see some negative camber on the wheels - be prepared for some tyre bills ......
Sorry about the waffle, love Cossies.....
Mike