Hey mate,
Most of the gold tours you see advertised over here are 7-10 days in duration and generally sold out by the start of the year. I do think there is a mob in Laverton that do a 3 day quad bike tour though-cant remember the name of them at the moment though. As for detectors, if you are going to spend money on a tour and a short one at that you would want to maximise your chances of getting gold by swinging a GPX i reckon, im pretty sure there is a few places over here you can hire them. Good luck when you get out there.