Hi Simon, sounds like there is still a lot of rules, wonder where they got the 100mm from the ground for the centre silencer? The way around it is to go to a an exhaust place that makes systems and get them to make you a new centre silencer that is either oval shaped or still round but smaller. From what you have said it sounds like it could do with a new system anyway. My Sapphire is lowered by 35mm so I had a custom made oval centre silencer made for mine as it used to ground out with the standard mongoose one.
My Brother-in-law lives in Salisbury and he worked at Holdens in Elizabeth where they made the HSV V8s. Last time He came over to visit us I took him out in my car and he was well impressed and said he thought it was a lot quicker than the HSVs! You will have fun in yours humbling some of the Aussie " performance " cars as most people there have no idea what your old 4 cylinder Ford is capable of!!! Mind you last time I was over there your cops are pretty hot on speeding so keep alert!
Cheers Richard.