Seat time.

Get a base PB around Barbs or RAC track and when you can no longer beat it look and changing something that will.
Rcomps would probably nett you the best result so maybe keep your 18s for daily and 17s for the track with some Rcomps ( cheaper by a fair bit compared to 18s )
After that a decent rear diff as you'll become frustrated with spinning the inside tyre on tight turns once you start exiting with decent speed.
No point changing shit if you don't know its helping.

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