Take a trip to bunnings. Add 1 petrol powered leaf blower and and a roll of duct tape. Seal the blower to the intake and you will have heaps more fun than any ebay turbo.
There are definitely gains to be made.
10-20kW can be gained on extractors alone.
Jump on preludeaustralia.com There are a lot of guys there that can help you with more specific info....
If its not the mounts or the transmission and the engine itself is running OK then maybe look at the clutch or flywheel??? Have you checked the side engine mounts? It could also be a cracked sub...
So far as restrictions go the main gains are at the header. Cat back gains would only be very small and normally only done to change the sound and appearance.
Given a choice go the manual.
They are getting on a bit now and will need some love and attention and $$.
Typical mechanical issues at about 300,000kms are main relay, CV joints, AC compressor,...
I don't think there is a lot you can do about it.
If you want a more precise shifter the best thing to do is make a true short shifter.
Flipmods (PA) can make these for you at a reasonable price.
IMO the 3g mounts are soft and a prone to a bit of wheel hop because of this.
It is not uncommon for them to crack the rubber and fail. Specifically the front and rear. The rear is the hardest to...
The standard wheel on a BA4/5 Prelude is 14"x5.5" with a +45 offset 4x100 stud pattern. The 4WS and non 4WS are the same offset. Some European models got 13" rims (not seen here).
Depends what you are out to achieve. 35mm is a good compromise and shouldn't cause too many issues with speed bumps, driveways etc. 50mm looks great, but just because the ride is stiffer doesn't mean...