Given that its a multanova not a laser, you have way less chance of getting out of it.
Lasers are humanly operated by cops, so there is always room for human error and also the fact that cops are 99% of the time only trained in the use of the laser equipment and not certified to calibrate it. Therefore if the cop was the person who calibrated the unit and they are not certified to do so... you would have a point to argue.
Multanovas are setup by radar operators (not cops) and are trained to set them up correctly. There are ways that the units can produce incorrect speed readings, such as:
1) if you were changing lanes at the exact time of the photo
2) if there is large cyclone type fencing or metal side railings, etc... anything that could interfere with a radio signal
Because they are setup by qualified people and are a "set and forget" device (aka no human operation) there is little room for error and your own arguments will not get you off without hard evidence like GPS tracking log or something.
You could try and contact Roy Reyer in QLD and see if you can obtain his services... he is often in court as a expert in the radar field... but he doesn't come cheap, and do you really want to pay for a QLD to Perth and return air fare???!!!
My suggestion would be to pay the fine, and buy a radar detector off me!!!