Aussie four door r31's have a tendancy to handle like a boat. Suspension is one thing I recommend. Extractors, Zorst and Pod do well. Keep your ignition system in good nic and it'll definately move better.
My r31 sits real high at the moment and handles like a Toyota Landcruiser. have to slow down for every corner. but it does help when i want to drive over things!
-jim