Hi, where in Sydney are you?
As for the carb you could try both but since you have a stock converter I would lean towards the 600 Holley. I would also send it to Greg Kuchel @ Carby Tuning Techniques to go through and mod/set up for best operation.
Have you put the Charger on the scales at WSID? My AP5 weights 3400lbs with a full tank of fuel so I doubt the VK is 3200Lbs
If you are interested I have 3200 stall converter.