This sounds much the same as the Harrison set up. The rear brakes do little in standard form. There is also a previous thread on this started by Sambo I believe. What some of us have done is to fit softer pads on the rear and change to the Falcon wagon master cylinder (about $180 from Repco). It has a different F/R bias and transforms the braking, or it did so on mine for road use. See forward and back in the thread:
Engineering tomorrow