Welcome to Just Commodores, a site specifically designed for all people who share the same passion as yourself.
For $300 you could do heaps to speed her up:
Take out the bellmouth: $0
Grind back the throttle-stopper: $0
Cut off the side of the standard airbox trunk, and open the mouth: $0
Grind off the rear muffler: $0
Take out the spare tyre, jack, back seats and door trim: $0
Cut down your springs to make the car more aerodynamic: $0
Steal a good performance memcal from a wreckers yard: $0
Get yourself a stage-2 B&M Shift-Kit, install yourself (if you have auto): $70
Get a good set of second-hand extractors: $230
and away you go